Guild Wars 2

Is there any way to wear a different, viewable helmet without wearing the headpiece of the baker’s and shadow assassin’s outfits?

Outfits are all-or-nothing. There’s no way to switch out any of the pieces for others, you have to wear the whole outfit and nothing but the outfit. You can hide certain pieces, but that’s the extent of the “customization” for outfits.

You can use the consumable halo or horns from the LS season 1.