If the other firm bought unlimited modules, you should be able to prepare that firm’s clients without incurring REP fees.  There are at least two approaches:

1 You can ask for backup of the client files from the other firm and restore the files to your desktop/laptop.  You should be able to process the client’s tax returns without incurring REP fees.

2 It is possible to install multiples firm files in Lacerte.  For the instructions, here is the link:

https://proconnect.intuit.com/community/help-articles/help/installing-multiple-firms-or-preparer-fil...

Either method should not cost you REF fees.