Tinkering with a 50cc moped as a hobby?

I was recently thinking about buying a 50cc moped and tinkering with it. Maybe adding new parts, personalizing it, wrapping it, and things like that. Just getting to grips with these engines, the technology, etc.

To what extent is this legally possible (do you have to register parts, etc.) and how much does it cost? Perhaps someone would like to share their experience in this area 👍.

Thanks