And now it seems like it’s set in stone in my Half Life… I was really enjoying playing Half Life and it’s mods… but… I can’t seem to bear it. I wanted to play the classic Redemption mod, but gave up when only the HD models were showing. It just doesn’t match the feel, and it doesn’t give me any nostalgia.
So turn it off. Did you not read the previous page?
Steam>Half-Life>Properties>BETAS>Steampipe.
Then Reinstall Half-Life. When it’s reinstalled there’ll be a little box in the video options to turn them off, so you can quit whining. 
Thought I tried that… Guess I’ll try it again and hope for luck.
edit: Well, the problem seems to be fixed for Half Life, but any mod I play (which is what I really want to do) still has the HD models. Really ruins the aesthetic for the mods.
Really? Re-install? That’s stupid, that means I would have to uninstall all of my other goldsrc games and re-install them
not even close
Or you could do the smart thing and move all of your mod folders until you reinstall HL.
Extract the LD models from the half-life GCF, they’re the originals, if you put them in the game or mod folder they’ll override the HD models. Do the same with the sounds and other files to revert all the changes. It might not work with some mods, you’ll have to check whether mods change some of the files.
Just play the WON version of half life.