I hear your concern..
Any major changes could have an impact on the warranty, if you have one (IMO)
Perhaps it would be a good alteration to install a shower and remove the tub for your use.
Keep in mind you are not going to gain a whole lot more head room for your tall husband.
There is 'handy'...then there is 'craftsman'.... depending on the quality of work it can hinder the resale price or it could improve the resale price, when the time comes.
I have done several modification to our RV's over time, but that comes with years as a boat and house finish carpenter career.
IMO... switching out a tub for a shower in an RV should be very doable with your husbands experience.
Just keep in mind to stick with RV components to complete the change.
Hope this helps
'07 WildCat 30 RLBS ~ West Coast Edition ~
Trail Air - Tri Glide Pin Box
2000 F350 Lariat DRW 4x4 7.3 Diesel 89k miles
Edge programmer, 4" SS exhaust turbo/back,
Tru-Cool Max Trans Cooler, Bilstein Shocks
Vancouver Island, B.C., Canada