KiCad’s libraries are read-only (for good reasons), so any footprint you want use more then once has to be put in a library you create yourself. (For one-offs you can load a footprint directly from the PCB into the Footprint Editor to modify it)
Once you’ve put a footprint in a library (and added that library to the library table) you can use as many instances of it as you like in all your projects.