When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
My dealer said it was okay to tint the windows, so bonnet stripes should be fine, but check with them to be sure. I had bonnet stripes on my black MINI for one year, then took them off and they left a faint shadow where the sun didn't shine. It's been 7 months since removal and I can't tell at all now.
Just a guess, but if you install anything that the dealer thinks "devalues" the car, you'll probably be hit for charges to remove it. Anything that is not a MINI item, or dealer option is probably subject to the dealer's opinion. If it doesn't decrease the value in the eyes of the dealer, they will probably take the car back, but I doubt they'll compensate you for it. Something like bonnet stripes, since they are a dealer option, would probably not hurt you. Underbody lights, I'd guess would hurt you on the return. Expessially if it in any way has put holes in the car, of voided any warrenties.