Originally Posted by C-IRVINE-94
If the author leaves the level as copyable then they don't mind if it's used by other people I think
Providing you say it's ok in the level description or via an in-game note, then it's absolutely ok to copy but you still have to be careful as sometimes copyright claims can be made and the mods will delete your level(s) as a result.
Another thing is, make sure your levels don't have any copyrighted material as they can be deleted sometimes by the mods.
I had some levels deleted a year or so back that I copied but no proper reason was given so be careful