Any question answered...

@Murphys_Law

I'm looking for a way to change the chainline on cranks for GXP bottom brackets.
More specific: I bought a Sram S300 crankset. It has a 41mm chainline. Since the chainring mounts on the inside and I am adding a thicker chainring I expect the chainline to drop to somewhere around 40mm.
I'd like to push that 1.5 mm outwards to get back into a more acceptable region.
I know you can shim the BB to affect the chainline, but I thought that was only possible for 73mm wide GXP BBs on 68mm wide BB-shells.
So how does this work?

You could trial the new chainring on the outer-side of the spider and stick a spacer behing the rear sprocket.