I know but I have the weekly rom from 6.12.22 which was miui 8.2 (the weekly roms got suspended afterwards because of android n). My question now is, can I just flash this stable rom over the 6.12.22 weekly (8.2 beta)?
No, I don't think so, weekly and Stable are 2 different developing rom ways, as far as I know you have to full wipe yor phone changing from one to another.