Most custom maps (or even all) don't ally anyone to clone their maps. Why? That is likely because they don't want their credit to be stolen from when they made that map since the new user who cloned that map will have the credits, so I have come up with an idea so that the original map-maker gets their rightful credit. (visual on the bottom) This will hopefully encourage the original map-maker to allow their maps to be cloned for other players to improve it.
What I propose is that the original map-maker's username stays under the cover image's icon, and next to the original map-maker's user name would say something like this, "(Adapted by [user])" or "(Modified by [user])".
In the following visual, I used Talos' Middle Earth map because it's the most popular custom map.
Visual: