The “don’t touch the lamp” thing is more related to incans, where finger print oils can cause thermal stresses in the glass and result in a fracture. That being said I would not go out of my way to touch the LED dome, or really “scrub” it unless it was unusually dirty for some odd reason. Its OK to just lightly dust it off though.
Cree emitters are pretty robust though. My builds have gone smoothly for the most part. One thing thing I have done more than once is nick the dome with a knife edge or soldering iron. I have to always remind myself to take it SLOWLY any time I am using tools around the LED.
So I try to avoid the LED dome because there’s no need to handle it, but is it that fragile? I’ve dropped them and they’ve rolled across the workbench plenty of times, and at the end of an emitter reflow to MCPCB I give the dome a flick to squeeze out excess solder - is this considered the acceptable exception to the rule? I’m a relative noob but I’ve yet to have a problem.