Begin playing around with a custom DataField for dice selection that will allow using the default AE modes on it

module/models/Actor/Player.mjs

@@ -1,4 +1,5 @@
 import DOTDUNGEON from "../../config.mjs";
+import { DiceField } from "../fields/DiceField.mjs";
 
 function diceChoiceField() {
 	return new foundry.data.fields.StringField({
@@ -38,7 +39,7 @@ export class PlayerData extends foundry.abstract.TypeDataModel {
 				integer: true,
 			}),
 			stats: new fields.SchemaField({
-				build: diceChoiceField(),
+				build: new DiceField(),
 				meta: diceChoiceField(),
 				presence: diceChoiceField(),
 				hands: diceChoiceField(),

module/models/fields/DiceField.mjs

@@ -0,0 +1,73 @@
+import { statDice } from "../../config.mjs";
+
+/**
+ * A subclass of StringField that allows ActiveEffects to integrate with dice
+ * values and increase/decrease the value step-wise according to the dice ladder.
+ */
+export class DiceField extends foundry.data.fields.DataField {
+	static get _defaults() {
+		return foundry.utils.mergeObject(super._defaults, {
+			trim: true,
+			blank: true,
+			initial: ``,
+			choices: [``, ...statDice],
+		});
+	};
+
+	constructor(options = {}, context = {}) {
+		super(options, context);
+
+		// v- because for some reason Foundry doesn't respect the _defaults getter
+		this.blank = true;
+		console.log(this.choices)
+	};
+
+	applyChange(...args) {
+		console.log(`DiceField.applyChange`, args);
+		return super.applyChange(...args)
+	}
+
+	_cast(value) {
+		return String(value);
+	}
+
+	_castChangeDelta(delta) {
+		console.log(`DiceField._castChangeDelta(${delta})`)
+		return parseInt(delta) ?? 0;
+	};
+
+	/** @inheritdoc */
+	_applyChangeAdd(value, delta, model, change) {
+		console.warn(`Cannot apply Add ActiveEffects to DiceFields. Not changing value.`);
+		return value;
+	};
+
+	_applyChangeMultiply(value, delta, model, change) {
+		console.warn(`Cannot apply Multiply ActiveEffects to DiceFields. Not changing value.`);
+		return value;
+	};
+
+	_applyChangeOverride(value, delta, model, change) {
+		return delta;
+	};
+
+	_applyChangeUpgrade(value, delta, model, change) {
+		console.log(`.dungeon | Pre: value=${value}; delta=${delta}`);
+		if (value === "") return value;
+		const dieIndex = statDice.findIndex(value);
+		const newIndex = Math.min(Math.max(0, dieIndex - delta), statDice.length - 1);
+		value = statDice[newIndex];
+		console.log(`.dungeon | Post: value=${value}; delta=${delta}`);
+		return value;
+	};
+
+	_applyChangeDowngrade(value, delta, model, change) {
+		console.log(`.dungeon | Pre: value=${value}; delta=${delta}`);
+		if (value === "") return value;
+		const dieIndex = statDice.findIndex(value);
+		const newIndex = Math.min(Math.max(0, dieIndex + delta), statDice.length - 1);
+		value = statDice[newIndex];
+		console.log(`.dungeon | Post: value=${value}; delta=${delta}`);
+		return value
+	};
+};