Friends, the shoulder pads are why it's here in 40K. Also, at least here in America, there is nothing wrong with making after market products! I could, if I cared to, build custom hoods (called "bonnets" over there, I believe) for Ford Mustangs. I could advertise them as being FOR Ford Mustangs (they wouldn't fit anything else in the known universe) and I wouldn't be impinging upon anyone's IP or need anyone's permission.

I can't express it any more simply than that. I completely agree with EldarGal that doing these things is neither reprehensible nor wrong. My custom hood ("bonnet") example is directly analogous to making shoulder pads for GW's Space Marines. Chapterhouse is perfectly within their rights to make custom shoulder pads FOR Space Marines. They don't need GW's approval and they aren't ripping anyone off.

It's hard to imagine that British laws are so different from American laws when it comes to aftermarket goods.