Would it be okay if I have a different layout for the home screen of the app before login + subscribing and after?
OK for who ?
For review, I see no interdiction in guidelines, except that :
3.1.1 In-App Purchase:
If you want to unlock features or functionality within your app, (by way of example: subscriptions, in-game currencies, game levels, access to premium content, or unlocking a full version), you must use in-app purchase.
3.1.2(a)
Apps must not force users to rate the app, review the app, download other apps, or other similar actions in order to access functionality, content, or use of the app.
3.1.2(c) Subscription Information:
Before asking a customer to subscribe, you should clearly describe what the user will get for the price. How many issues per month? How much cloud storage? What kind of access to your service?