I have been working in mobile development since last 5 years and developed many apps.
Developed apps: Photo/Video sharing, VoIP based, Fashion industry, Health related, Food, Social media, Location tracking and much more.
Still I am not not clear what you want to do exactly with app design/UX/UI but I have worked before something similar work like minor changes in design like text, logo, some icon etc and quick gave to client, After review another same app but with different texts,logo,icons etc.