Yes I would say it is possible to houserule just about anything. Really in any RPG, the GM/DM/referee/whatever can houserule to get the feel/effect they want - who can stop us?
But my own feeling so far is that it doesn't feel like I have to houserule, at least not as much anyway. Now TBH, this may be a misconception in part by me, due to the fact that GURPS is so customisable by design. This "customisation" doesn't feel like "houseruling", more like tweaking by choice than like fixing by necessity. However, that may just be my non-impartial feelings getting in the way