Fitting zetec s bumpers and side skirts and spoilers to my fiesta mk5 at the moment need some advise on best way to fit the side skirts

I have been told 3 options by various folks....

self tapping screws...sills are quite old and been underseal by myself (not rotted) but nervous make holes in them as could cause them to rot as the car is very old.
3m tape lol? is this really a valid option?
tiger seal to glue them on....? would this cause issues on MOT and in the future if they needed taking off?

another question is do i need to let my insurance know before adding these side skirts and different bumpers? (i assume i do and if so what problems could i face?) starting with the spoiler at the moment as smallest part to paint. will post photos soon.

btw this just a cheap diy upgrade to my car budget low im spray painting all bumpers myself not looking for it to be a master piece but bit better then it is now