Yes they are replaceable, but I wouldn't replace them if everything is working correctly. If you are unsure of your car's service history, it may me worth removing them and checking the plugs.
Or... just do something like the an m45 eaton supercharger from a mini cooper S or the M24 supercharger from eaton. Im sure you can find either on ebay pretty quickly.
From looking at this, if I were to get 2 U sections of 1" diameter piping, then this would be easy to replicate? You can weld to the OEM manifold also, which looks pretty awesome.
I like this idea a lot!!!
Seats in! Also I'll upload pics on the bracket. This is my first time, but I'll put a proper Diy together. They do sit a little off center, and it annoys me. I may work something out to fix that.