Whoops, I shouldn’t have used the word “method” as it has multiple meanings here. I understand that the API methods are well documented, I meant the method (as in technique/solution) that you shared uses those APIs in a clever way that doesn’t seem to be mentioned anywhere and is only obvious if you already know about it.
After switching the -n technique to your given InsertService technique, I was met with this:
InsertService cannot be used to load assets from the client
The workaround you provided doesn’t work on the client, which is extremely inconvenient.
After reworking it to be on the server, I found that this suggested workaround is still does not work, since InsertService cannot insert assets that you don’t own.
HTTP 403 (Forbidden)
An asset loaded by this function must be created or owned by either the game creator or Roblox. (Source)
The goal in our aforementioned use cases is to allow players to use custom images that they own, so this completely defeats the purpose.
So, unfortunately, my original post’s method is still the only currently available hack.