If you have project specific libraries, you could have entered their location as either absolute or relative path in
Preferences / Manage Symbol Libraries
Preferences / Manage Footprint Libraries
Both dialogs have 2 tabs, and the right tab is for "Project specific Libraries".
There you can use ${KIPRJMOD} to point to the current location of the active project.
All KiCad's files are human readable ascii.
I've made good use of this with search and replace operations a few times, for example for changing some symbols or footprint references to different libraries.
But as KiCad's own interface is ever improving this is less and less necessary.