Good, but I want the bathtub01a from Left 4 Dead hexed to bathtub01b because there already is a bathtub01a in source models.gcf. Even some things in the left 4 dead props spawnlist are the same models as HL2, you gotta hex garbage_coffeemug001a from L4D into garbage_coffeemug001b which also has the same model name in source models. The milkcarton is also wrong, hex too into a b instead of a and these 3 below:
Gascan from Left 4 Dead 2 should be hexed to gascan001b for several reasons
Same for propanecanister and the shoe001a
Sorry, but HL2 and every game mounted by GMod has priority over L4D2. All you can do, as suggested, is hexing the model manually.