I dont think there are any quest functions to do that. Since you probably dont care about the individual, you can just run a vague query to set all players in those guilds bankers. Something like:
Code:
UPDATE guild_members SET banker = 1 WHERE (guild_id = 30 || guild_id = 31 || guild_id = 32 || guild_id = 33);
In order to run a query through Perl you first need to make a connection with the DBI module. If you don't know how to use the DBI module there are a few posts with examples.