I'm still working out how I want to tweak this before I replicate the changes on the type 1 Golden Lunehelm (Gold Rathian sallet), but HOLY SHIT I FINALLY FIGURED OUT HOW TO DO THE THING I DOWNLOADED BLENDER FOR IN THE FIRST PLACE!!!! The original attempt at this change went...... poorly, to say the least, because I didn't realize that what I was deleting was apparently load-bearing for the helm's ability to latch onto the head's rigging.
I gave up on it for a while because I mistakenly thought that even if I could get it to remain properly rigged, the limitations of .user.2 files (which tell the game how to modify the hunter's base model, usually relating to the head and hairstyle) would prevent it from working unless I took the time to alter the model to fit the size of a hunter's normal head. Turns out that was completely unnecessary! By shrinking the bevor to fit inside the player's head, it maintains the rigging, and it turns out the helm is large enough for the hunter's full-size noggin! I need to experiment with .user.2 files to make sure there's no better option than the type 1 Vespoid helm's file that I'm currently using (I'd previously used the type 2 Ceanataur helm's file, which might work better? The Alloy helm also comes to mind, and there are probably a few others too), and I might want to tweak the visor a bit further, but overall I'm quite chuffed with how this has turned out. I've always been a fan of the "sallet with the mouth exposed" look, going all the way back to high school when I first took an interest in historical armor. Sadly I don't have the modeling and texturing chops to add a chinstrap, but that's hardly the end of the world.
(I'm back on my "take screenshots with Best and Prettiest Sunbreak Character™ Dame Fiorayne" bullshit now that I've successfully finished editing the models for these helms)
I've always loved that overall look in the first image, i.e. a sallet with a lowered visor but no bevor, and a big ol' scarf wrapped around the neck, so I'm really glad I finally have armor that'll let me pull it off (sadly the scarf is necessary for a lot of armors because the gorget sits REALLY high, but that's true of a lot of helms)
Realizing I may have to learn how to edit .user.2 files if I want to use anything more complex than the type 1 Vespoid or type 2 Ceanataur ones (which are both super restrictive on what hair they allow to exist) 
(Or if they have it's somewhere I haven't thought to look )
Really not looking forward to spending several hours trial-and-erroring my way through making this shit work with no context for what any of it means while trying to make a few VERY small changes to the type 2 Aknosom Helm S .user.2 file to smush down the hunter's bangs and maybe be a little more lenient with ponytails (or alternatively I might modify the Jyuratodus Helm S one since that allows the ponytail the way I'd want, but it has more to smush/hide)