EDIT: Beat to it.

Once again:

You have a level 50 BLM. You want to play an alt in the Wolves' Den. Right on! Here's what you can do:

- Use the armory system. Level a MNK on the same character you have your BLM on. Every time you want to switch classes, you need to play 180 matches to afford it.

- Create a new alt character and level your MNK there. You can now play both classes as you please, all it takes is the 30 seconds you need to relog. Needless to say, not having to spend 180 matches worth of currency simply on respeccing will actually allow you to buy some PvP gear if you pick this option.