They've worn out the skin around their butthole a little bit with all the sits baths and shower head use?
I have been taking sitz baths and using the showerhead to clean my butt after BMs for the better part of a year now and the skin around there feels thinned out and sensitive.
Will that skin toughen back up in the months and years after surgery because I'll be taking many less baths and not using the showerhead as TP anymore?

I don't think it will thin out with water, logically it shld be using toilet paper that wears out the skin. In fact, it's our fissures that cause our anus to be more sensitive than ever before, that's my views

I agree with dwarfs8. Fissures definitely cause more sensitivity and irritation! I also think all the warm baths and water seem to dry out the skin.
Since surgery I rarely use toilet paper and I still use the shower wand periodically through out the day but I've only been taking a bath once a day for months now and sometimes just take a shower and forget the baths. It does get stronger lurker. It seems to take some time though. I often apply vaseline when it just feels dried out down there. I know my legs and the rest of my body needed more lotion than usual when I was having all the long warm baths...

cotton balls are a good alternative to TP