I suppose it isn't intuitively obvious. The lines you want to edit are in the EDB (export_descr_building.txt). The recruit line looks like this:
Code:
recruit_pool "Musketeers" 1 0.5 4 0 requires factions
{ spain, portugal, milan, venice, } and event_counter gunpowder_discovered 1
That 0.5 is what you want to edit. This effects the "recruit pool replenishment" rate. The higher the number, the faster it fills. I put it at 0.2 and was generating a new musketeer every three turns. At 0.9 I as getting about one a turn. I think at 0.5 you get one more every three turns or thereabouts. Play around with it.
The 4 is the size of the "recruit pool". I don't know if there is a limit. Most recruits don't get a pool bigger than 6 but mercenary recruits go as high as 12 in some places.