I had mine trimmed (cut) about 1/4” on the rears. I’m running 17mm spacers with oem 20” Tornadoes, Michelin PS4s, and VAP lowering springs. My last Ftype (lease) with 15mm spacers, VAP springs, and PS4s rubbed a little on big compressions, so I removed spacers on rears... but the new setup with the rear fenders trimmed has had no rubbing. They cut 1/4”, smoothed it and used touch up paint (but you can’t see it unless you lay on your back against the wheel, anyway).

I work with aluminum everyday restoring WW II aircraft. We do a lot of fabrication with aluminum and though the nature of the processes are beyond the scope of this site, I’ll just confirm what Tork Master mentioned- aluminum is not as tolerant to being shaped as steel, and will crack easily if done incorrectly. Even though the aluminum sheets used during the stamping process were the originally in annealed (soft) condition, the forming process causes them to work harden. Aluminum also age hardens in time after being worked. Don’t think aluminum doesn’t, corrode it’s actually very active. Start removing the paint with a die grinder and you have exposed the metal to road salts, corrosive environmental conditions and good old oxygen, which is trying to convert the metal to aluminum oxide. Aircraft aluminum skins actually have a layer of pure aluminum plated over the aluminum alloy to serve as a sacrificial layer against corrosion. The metal our cars are made of do not have this, so the only protection the metal has is special etching,primers and paints.