Base size question

I couldn't find anything official but am I allowed to change the base size for my models?
In particular am I allowed to change all my hq bases from 25 to 32 mm and would that be legal?

I actually recently realized for most competitive events like NOVA, Adepticon etc. you need to have the proper base sizes, so 25mm for all Drukhari characters. Bummer for me since I based some of my converted characters on 32mm. Everyday casual play though, and even small local tournaments, I've never had anyone hassle me about my base sizes, it is for just 2 characters.

Official GW ruling, I'm not actually certain.