Hi,
Currently, it's not possible, and generally I strongly advice to never touch any assets coming from external sources, assets store, etc... it always comes back to bite you at some point.
I know it's a pain... what I do is that I create a "App" or "MyGame" folder and there I put all my stuff, I never put anything in the Assets folder root that is specific to a particular project, only assets coming from packages.
Bye,
Jean