Minimodding was actually a point of contention the last time we revised the rules. There's no "official" definition of minimodding (it's not like it's in a real dictionary), and Urban Dictionary defines it as "someone who isn't a moderator but tells other people how to conduct themselves", but I've heard other people say that telling others things are against the rules is fine as long as you don't threaten muting/banning.
So the simple answer is: we haven't really decided whether or not that's okay.
The rules are currently worded to be unclear, too... :/
I guess I'll make an executive decision and say that warning (but obviously not threatening mutes/bans) is okay for voices.
Pokemon Showdown | Replay player | No, I am not impressed that you know that my name is Guangcong Luo. The PS website says "Copyright Guangcong Luo" at the bottom, ffs.