I have a Custom 823 and like to use it both with a FA nib and the original, M nib. I change nibs by gently twisting them out (friction fit, but the "unscrewing" motion seems to work better then just pulling out the nib).

If I do this alot, meaning change the nibs once a week or once a month, will it cause problems, like weakening the fit of the nib?

Can't you just swap the whole section? Would save you messing with something that is not meant to be messed with...

The 823 is a vac-filler, so the section is not normally removable.

I can't say whether repeated nib swaps would be bad in the long term. I've only done it a couple of times with my 823, for cleaning. I imagine if you're careful it would probably be OK, but I'm reluctant to try it too often with mine.