Seems that your request is already anticipated in the scripts fmSpark uses to create the journal entries.
The script "create journal entry" (in fmSpark's "[ MESSAGES ]" section of scripts) contains a branch where you can create records in a second journal table depending on which
Merge Group your message is related to.
So, create your new journal table by duplicating the one you're already using for Customers and then duplicate the script "New Action..." in your file, modifying it to create new records in this new journal table.
Now return to fmSpark and edit the "create journal entry" script, finding the comment "----- Duplicate script steps below for new GROUP -----". Edit the ElseIf() line that follows to use the name of your second merge group (the one for leads).
Continue editing this script to call your second version of the "New Action..." script right after the comment "call journal creation script in "YOURFILEHERE" file".
The script's comments are pretty good: better than my explanation above.
