Please explain your feature request to the best of your abilities:

Currently for re-balancing and calculating who should be at the site (for non involvement TP away) it just uses online town members.

I would like it to be online town members who have the "towny.command.town.defend" permission.

This way, if admins want all town members just like it stands, they can leave that perm in the default group. But it would also allow admins to create fighter ranks for towns to select, which means they can choose who is allowed to fight and who is part of the re-balancing calculations.