No there won't be, this is not a fantasy MMO where you can magically make a helmet disappear just cause you don't like it, but retain the stats.
There is a balance of realism and fantasy that makes TES games so great... and a toggle would kill this.
Either way, you read the perks wrong, only one forces you to wear a matching set, the others a mis matched... not to mention the perks are stats that are not needed... so don't wear a helmet no big deal.
A lot of single player RPGs have this option, so it's in no way unique for the MMO genre.
If there was a toggle, you would have the option not to use it. Also, it's a single player game and the toggle would only affect YOUR helm, so it's not like there's going to be a lot of other people running around without helms ruining your sense of immersion or whatever.
Okay. That's not what it says in http://www.gamesas.com/index.php?/topic/1249457-light-armor-perks/ thread.
I'm not usually a fan of the Hide/Show Helmet toggle, but IF the OP of that thread is correct, then I'll definitely want one. I guess I'll just have to wait for a mod.