diff --git a/src/sim/transactions.ts b/src/sim/transactions.ts
index 047d112..6a104c7 100644
--- a/src/sim/transactions.ts
+++ b/src/sim/transactions.ts
@@ -2,7 +2,7 @@ import { Catalog, getGame } from './catalog';
 import { customerMinimumAsk, priceOf } from './economy';
 import { Customer } from './customers';
 import { addToBackroom, getSlot, ItemRef, takeFromSlot } from './inventory';
-import { addStamp, currentProgram, issueCard, joinProbability, Reward, StampType } from './loyalty';
+import { addStamp, currentProgram, issueCard, joinProbability, Reward, setProgram, StampTrack, StampType } from './loyalty';
 import { random } from './rng';
 import { adjustReputation, GameState } from './state';
 
@@ -128,6 +128,12 @@ export function trade(
   return { accepted: true, customerPaysCents, shopPaysCents, voucherGivenCents };
 }
 
+/** Replaces the loyalty program and applies the reputation penalty for a less generous one. */
+export function changeLoyaltyProgram(state: GameState, tracks: StampTrack[]): void {
+  const { reputationDelta } = setProgram(state.loyalty, tracks);
+  adjustReputation(state, reputationDelta);
+}
+
 export function recordLostRequest(state: GameState): void {
   state.day.lostRequests += 1;
   adjustReputation(state, -1);
diff --git a/tests/sim/transactions.test.ts b/tests/sim/transactions.test.ts
index f7dab32..41cba3d 100644
--- a/tests/sim/transactions.test.ts
+++ b/tests/sim/transactions.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { buyBack, recordLostRequest, recordSatisfiedRequest, sell, trade } from '../../src/sim/transactions';
+import { buyBack, changeLoyaltyProgram, recordLostRequest, recordSatisfiedRequest, sell, trade } from '../../src/sim/transactions';
 import { createNewGame } from '../../src/sim/state';
 import { backroomQty, getSlot } from '../../src/sim/inventory';
 import { issueCard, setProgram } from '../../src/sim/loyalty';
@@ -198,3 +198,20 @@ describe('reward and cash edge cases', () => {
     expect(s.day.trades).toBe(0);
   });
 });
+
+describe('changeLoyaltyProgram', () => {
+  it('lowers reputation by 2 when the program becomes less generous', () => {
+    const s = createNewGame(1);
+    s.reputation = 50;
+    changeLoyaltyProgram(s, [{ stampType: 'buy_new', slots: 20, reward: { kind: 'voucher', valueCents: 500 } }]);
+    expect(s.reputation).toBe(48);
+    expect(s.loyalty.programs).toHaveLength(2);
+  });
+
+  it('leaves reputation unchanged when the program is more generous', () => {
+    const s = createNewGame(1);
+    s.reputation = 50;
+    changeLoyaltyProgram(s, [{ stampType: 'buy_new', slots: 5, reward: { kind: 'voucher', valueCents: 1000 } }]);
+    expect(s.reputation).toBe(50);
+  });
+});