Yes. But why would you want to?
You can see the equivalent on thrustcurve.org here: https://www.thrustcurve.org/outbox/filesets/. There's one giant file for each manufacturer.
Thanks all'Y'all !If you add the folder they're contained in into the dialog, you don't have to add them individually.
I copied my l-o-n-g explicit list of individual motor files into a directory: /home/konrad/.openrocket/ThrustCurves/
Then I cleared the long list of explicit .eng files from the [Edit]->[Preferences] Dialog and repaced the list with the directory and restarted OR.
After a couple false-starts where I missed a couple files, I now have only the single directory entry instead of an ever-growing list of .eng files.
Thanks again for the tap with the clue-stick
-- kjh