I am hoping to find a way to attach my metal house numbers to facia clad with metal sheathing without damaging the metal. the
Automotive trim tape.
For example, 3M 38583 (I'm not in any way associated with 3M, but I did just buy a roll of the stuff for the automotive purpose it's intended for.)
Weatherproof, lasts a long time, and if you need to remove them you saw them off with a section of fishing line and then rub the remaining adhesive off (they even make a special tool for THAT job for the automotive application, but I haven't bought one as I doubt the scale of my job calls for it.)
If the metal is steel, then magnetic vinyl/rubber sheet