Hekatrix/wyches with hellglaives for fluff, against the rules?

I'm new to the Warhammer Universe, and I have yet to play my first game, and I'm currently working on my first Kabal. I know little about the game in general expect for the very basics, that I have learned by lurking different forums and such.

I've got 2 wyches and a hekatrix with Hellglaives, and I was wondering if it's possible to use them as regular wyches/hekatrix/w splinter pistol/VB if i've got an army sheet that clearly states what they are? I know it might be acceptable at local GW games, but what about tournaments and such? Does it break the WYSIWYG, thus rendering those models useless for anything than a sexy shelf?

WYSIWYG is enforced semi-loosely in the grand scheme of things.
Rule of Cool (does it look awesome) seems to be a stronger rule in general.

If you paint the Hekatrix's glaive so it looks different from the Wych glaives (and to be a venom blade I would submit you would probably want to paint it so it looks like it is a poison blade in some way at a glance) then you should be perfectly fine. You might have a bit of issue with persnickity gamers running the one glaive as a v.blade and the others as regular CCWs if the paint scheme is identical - but even then I would suspect most would be fine with it.

Was already planning on making the sides of the VB green . But this is awesome, might submit pics when they're done :>

A good question I hadn't considered. I know In Warhammer Fantasy there's a rule that states whatever the unit's majority of models represents (modeled as), that is how the unit is considered to be armed.....as it's ok for a minority of the unit to modeled differently. I just don't know if that applies in 40K too. This is similar to a question I had about conversions; as long as the majority of the model is GW product its acceptable.

the reason for that Sathonyx is units have multiple weapon options (take brets Men at Arms, who can be armed with either hailbards or spears) In 40k normally a chunk of the unit is armed the same, with 1~2 specials and a sargie. Ofc there are units that dont do this (think ork nobs or SM vets) but most troops are about the same.

That being said, as long as I can tell what they should be, and who is special in the unit, I would have no problem with it