Fun and Balance is available updated for 1.13.1:
- Fun and Balance for EU4 1.13.1 - Download. Steam Workshop
- Fun and Balance for EU4 1.13.1 and Extended Timeline (0.13.6 version) - Download | Steam Workshop
It's been surprisingly common that people playing Fun and Balance mod get early access to features which vanilla players only see many versions later - the biggest one was probably pushing vassals' CBs, but all kinds of changes I make end up being unnecessary a few versions later.
As with other government type change decisions, Fun and Balance removes number of provinces restrictions, but you still need to do fulfil other requirements (religious and diplomatic ideas fully filled).
Enjoy the games!