Using the how to guides here, I just completed a Mini D2S Retrofit and black headlight mod, using hardware purchased off of TRS. The guides available here and at HIDplanet make it VERY easy for a DIYer. I thought I'd just add my $0.02 to some of the issues/problems I ran into for the next guy.
1st step: remove headlight assemblies. The #1 biggest issue here is getting one particular bolt off -- it's lateral attached to the fender -- a real PITA. The only way I could do it was to take off my bumper. I didn't bother putting that 1 bolt back on when I re-installed the headlights. I just put some black RTV silicone gasket maker on the end.