What Hoshichiri is really asking for is a feature request and doesn't know it. And that is: rather than link an existing db entry to a personal collection, have the option to upload a custom image. That would allow you to add any stock GBA (you'd still need to pick one) but then upload a different picture to the entry. A picture that would only appear when viewing your collection.
Well, sort of- what I want is the listing for this particular GBA to not specify a color it isn't. I don't care if the photo is of my specific unit or not- I don't mind pointing out the mods in the notes panel. I just don't want some hypothetical visitor looking at my collection to see 'HoshiChiri has 3 GBAs, 2 indigo & 1 fuchsia.' I want them to see 3 GBAs, 1 indigo, 1 fuchsia, 1 custom (since I don't know anything beyond that for its origins).
I can get proper photos up later, but the shell is
here, which shows pretty well what my unit looks like. I bought it from retromodding.com, their custom build page is
here. Just to demonstrate the full origins of the unit to my knowledge.
(Also, thanks to whatever mod pulled this into its own topic, I appreciate that.)