Start on migration handlers

module/systemRegistration/migration-handlers/2_5_2.mjs

@@ -0,0 +1,35 @@
+export class Migration_2_5_2 {
+    version = '2.5.2';
+
+    async updateEffect(effectSource, item) {
+        let shouldUpdate = false;
+        const newChanges = [];
+        const srdItem = item?._stats.compendiumSource ? 
+            await foundry.utils.fromUuid(item?._stats.compendiumSource) : 
+            null;
+        for (let i = 0; i < effectSource.system.changes.length; i++) {
+            const change = effectSource.system.changes[i];
+            const srdEffect = srdItem?.effects.find(x => x.name === effectSource.name);
+            if (change.type === 'custom') {
+                const srdChange = srdEffect ? srdEffect.system.changes[i] : null;
+                if (
+                    change.key === srdChange.key && 
+                    change.value === srdChange.value && 
+                    change.type !== srdChange.type
+                ) {
+                    shouldUpdate = true;
+                    newChanges.push(srdChange);
+                }
+            } else {
+                newChanges.push(change);
+            }
+        }
+
+        if (shouldUpdate) {
+            return {
+                _id: effectSource._id,
+                system: { changes: newChanges }
+            }
+        }
+    }
+}