Motability allow aftermarket tints (legal) however, if your window needs replacing the cost to replace the tints is down to you.
Roof box/rack is allowed r upto the manufacturers maximum loading weight
Go faster stripes mmm? I’d speak to Motability (I was allowed a black wrap on the roof of my last car)
Factory or dealer fitted sidebars/steps would be allowed. Aftermarket again speak with Motability.