I have a nice thick head full of hair, not particularly long (gets longish at times), just kinda wavy, but dark & thick…so…
…if I dusted off the clippers & gave myself a no. 2, would I need a smaller helmet?
Currently using a Bell Ghisallo (M) & a LG Rocket (L).
Thank you for your time.
Can’t you just adjust it a little?
Sure, and the Bell would probably be good. The Rocket though is borderline big to begin with…the only model I could squeeze over ears (I have a wide head!). I guess I was just looking for anyone out there whose done the same (drastic hairstyle change) and thought “fuck, my helmet doesn’t fit now!” 
Its a pretty dumb question I know, but decent helmets (particulalry aero) are really expensive here…
Well then, I don’t know. I was not blessed with thick hair. Even if I were, not likely I take clippers to my head.