Chance of Spam Rejection

I’m reviewing the developer guidelines and I’m just wondering if anyone has any personal experience. My app is finding moderate success, I’m thinking I can apply the same formula to a different niche. The apps fundamentally work the same but in different categories to serve completely different purposes, so naturally the UI would be similar. How much do I need to “change” my new app to avoid a spam rejection? Without Apple review I’d be able to just use my old app like a template and adapt it to the new niche but it seems like a slippery slope for rejection. Thanks