diff --git a/ftl/core/deck-config.ftl b/ftl/core/deck-config.ftl
index bbc7ac222..5b4551b6b 100644
--- a/ftl/core/deck-config.ftl
+++ b/ftl/core/deck-config.ftl
@@ -173,6 +173,8 @@ deck-config-interval-modifier-tooltip =
 deck-config-hard-interval-tooltip = The multiplier applied to a review interval when answering `Hard`.
 deck-config-new-interval-tooltip = The multiplier applied to a review interval when answering `Again`.
 deck-config-minimum-interval-tooltip = The minimum interval given to a review card after answering `Again`.
+deck-config-custom-scheduling = Custom scheduling
+deck-config-custom-scheduling-tooltip = Affects the entire collection. Use at your own risk!
 
 ## Adding/renaming
 
diff --git a/rslib/backend.proto b/rslib/backend.proto
index 7d72276b4..df595c666 100644
--- a/rslib/backend.proto
+++ b/rslib/backend.proto
@@ -965,6 +965,8 @@ message DeckConfigsForUpdate {
   bool schema_modified = 4;
   bool v3_scheduler = 5;
   bool have_addons = 6;
+  // only applies to v3 scheduler
+  string card_state_customizer = 7;
 }
 
 message UpdateDeckConfigsRequest {
@@ -974,6 +976,7 @@ message UpdateDeckConfigsRequest {
   repeated DeckConfig configs = 2;
   repeated int64 removed_config_ids = 3;
   bool apply_to_children = 4;
+  string card_state_customizer = 5;
 }
 
 message SetTagCollapsedRequest {
@@ -1470,6 +1473,7 @@ message Config {
       SET_DUE_BROWSER = 0;
       SET_DUE_REVIEWER = 1;
       DEFAULT_SEARCH_TEXT = 2;
+      CARD_STATE_CUSTOMIZER = 3;
     }
     Key key = 1;
   }
diff --git a/rslib/src/backend/config.rs b/rslib/src/backend/config.rs
index f28a43d86..d17feb53b 100644
--- a/rslib/src/backend/config.rs
+++ b/rslib/src/backend/config.rs
@@ -43,6 +43,7 @@ impl From<StringKeyProto> for StringKey {
             StringKeyProto::SetDueBrowser => StringKey::SetDueBrowser,
             StringKeyProto::SetDueReviewer => StringKey::SetDueReviewer,
             StringKeyProto::DefaultSearchText => StringKey::DefaultSearchText,
+            StringKeyProto::CardStateCustomizer => StringKey::CardStateCustomizer,
         }
     }
 }
diff --git a/rslib/src/backend/deckconfig.rs b/rslib/src/backend/deckconfig.rs
index 2820bfcd8..53db0ca05 100644
--- a/rslib/src/backend/deckconfig.rs
+++ b/rslib/src/backend/deckconfig.rs
@@ -88,6 +88,7 @@ impl From<pb::UpdateDeckConfigsRequest> for UpdateDeckConfigsRequest {
             configs: c.configs.into_iter().map(Into::into).collect(),
             removed_config_ids: c.removed_config_ids.into_iter().map(Into::into).collect(),
             apply_to_children: c.apply_to_children,
+            card_state_customizer: c.card_state_customizer,
         }
     }
 }
diff --git a/rslib/src/config/string.rs b/rslib/src/config/string.rs
index 10da7c206..edf42c868 100644
--- a/rslib/src/config/string.rs
+++ b/rslib/src/config/string.rs
@@ -11,6 +11,7 @@ pub enum StringKey {
     SetDueBrowser,
     SetDueReviewer,
     DefaultSearchText,
+    CardStateCustomizer,
 }
 
 impl Collection {
diff --git a/rslib/src/deckconfig/update.rs b/rslib/src/deckconfig/update.rs
index 66df07e72..3007046b3 100644
--- a/rslib/src/deckconfig/update.rs
+++ b/rslib/src/deckconfig/update.rs
@@ -11,6 +11,7 @@ use std::{
 use crate::{
     backend_proto as pb,
     backend_proto::deck_configs_for_update::{ConfigWithExtra, CurrentDeck},
+    config::StringKey,
     prelude::*,
 };
 
@@ -21,6 +22,7 @@ pub struct UpdateDeckConfigsRequest {
     pub configs: Vec<DeckConfig>,
     pub removed_config_ids: Vec<DeckConfigId>,
     pub apply_to_children: bool,
+    pub card_state_customizer: String,
 }
 
 impl Collection {
@@ -39,6 +41,7 @@ impl Collection {
                 .schema_changed_since_sync(),
             v3_scheduler: self.get_config_bool(BoolKey::Sched2021),
             have_addons: false,
+            card_state_customizer: self.get_config_string(StringKey::CardStateCustomizer),
         })
     }
 
@@ -178,6 +181,8 @@ impl Collection {
             }
         }
 
+        self.set_config_string_inner(StringKey::CardStateCustomizer, &input.card_state_customizer)?;
+
         Ok(())
     }
 }
@@ -199,6 +204,9 @@ mod test {
             col.add_note(&mut note, DeckId(1))?;
         }
 
+        // add the key so it doesn't trigger a change below
+        col.set_config_string_inner(StringKey::CardStateCustomizer, "")?;
+
         // pretend we're in sync
         let stamps = col.storage.get_collection_timestamps()?;
         col.storage.set_last_sync(stamps.schema_change)?;
@@ -228,6 +236,7 @@ mod test {
                 .collect(),
             removed_config_ids: vec![],
             apply_to_children: false,
+            card_state_customizer: "".to_string(),
         };
         assert!(!col.update_deck_configs(input.clone())?.changes.had_change());
 
diff --git a/ts/deckoptions/AdvancedOptions.svelte b/ts/deckoptions/AdvancedOptions.svelte
index ed953b260..62640889c 100644
--- a/ts/deckoptions/AdvancedOptions.svelte
+++ b/ts/deckoptions/AdvancedOptions.svelte
@@ -9,12 +9,14 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
     import SpinBoxRow from "./SpinBoxRow.svelte";
     import SpinBoxFloatRow from "./SpinBoxFloatRow.svelte";
     import type { DeckOptionsState } from "./lib";
+    import CardStateCustomizer from "./CardStateCustomizer.svelte";
 
     export let state: DeckOptionsState;
     export let api: Record<string, never>;
 
     let config = state.currentConfig;
     let defaults = state.defaults;
+    let cardStateCustomizer = state.cardStateCustomizer;
 </script>
 
 <TitledContainer title={tr.deckConfigAdvancedTitle()} {api}>
@@ -88,4 +90,10 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
             {tr.schedulingNewInterval()}
         </SpinBoxFloatRow>
     </Item>
+
+    {#if state.v3Scheduler}
+        <Item>
+            <CardStateCustomizer bind:value={$cardStateCustomizer} />
+        </Item>
+    {/if}
 </TitledContainer>
diff --git a/ts/deckoptions/CardStateCustomizer.svelte b/ts/deckoptions/CardStateCustomizer.svelte
new file mode 100644
index 000000000..c9dc2a0e3
--- /dev/null
+++ b/ts/deckoptions/CardStateCustomizer.svelte
@@ -0,0 +1,37 @@
+<!--
+Copyright: Ankitects Pty Ltd and contributors
+License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
+-->
+<script lang="ts">
+    import * as tr from "lib/i18n";
+    import TooltipLabel from "./TooltipLabel.svelte";
+    import RevertButton from "./RevertButton.svelte";
+    import Row from "./Row.svelte";
+    import Col from "./Col.svelte";
+
+    export let value: string;
+</script>
+
+<Row>
+    <Col>
+        <div class="text">
+            <TooltipLabel markdownTooltip={tr.deckConfigCustomSchedulingTooltip()}>
+                {tr.deckConfigCustomScheduling()}:</TooltipLabel
+            >
+            <RevertButton bind:value defaultValue="" />
+        </div>
+    </Col>
+</Row>
+
+<textarea bind:value />
+
+<style>
+    .text {
+        min-height: 2em;
+    }
+    textarea {
+        width: 100%;
+        height: 10em;
+        font-family: monospace;
+    }
+</style>
diff --git a/ts/deckoptions/deckoptions-base.scss b/ts/deckoptions/deckoptions-base.scss
index 88a64a3c6..47bbdd1fe 100644
--- a/ts/deckoptions/deckoptions-base.scss
+++ b/ts/deckoptions/deckoptions-base.scss
@@ -44,3 +44,8 @@ $tooltip-max-width: 300px;
         color: #ffaaaa;
     }
 }
+
+textarea {
+    color: var(--text-fg);
+    background-color: var(--frame-bg);
+}
diff --git a/ts/deckoptions/lib.ts b/ts/deckoptions/lib.ts
index b51762424..3ca866df6 100644
--- a/ts/deckoptions/lib.ts
+++ b/ts/deckoptions/lib.ts
@@ -55,6 +55,7 @@ export class DeckOptionsState {
     readonly currentAuxData: Writable<Record<string, unknown>>;
     readonly configList: Readable<ConfigListEntry[]>;
     readonly parentLimits: Readable<ParentLimits>;
+    readonly cardStateCustomizer: Writable<string>;
     readonly currentDeck: pb.BackendProto.DeckConfigsForUpdate.CurrentDeck;
     readonly defaults: ConfigInner;
     readonly addonComponents: Writable<DynamicSvelteComponent[]>;
@@ -88,6 +89,7 @@ export class DeckOptionsState {
         );
         this.v3Scheduler = data.v3Scheduler;
         this.haveAddons = data.haveAddons;
+        this.cardStateCustomizer = writable(data.cardStateCustomizer);
 
         // decrement the use count of the starting item, as we'll apply +1 to currently
         // selected one at display time
@@ -210,6 +212,7 @@ export class DeckOptionsState {
             removedConfigIds: this.removedConfigs,
             configs,
             applyToChildren,
+            cardStateCustomizer: get(this.cardStateCustomizer),
         });
     }