you can indeed create two Behaviours for one app. I wouldn't see why 
this should not work. You should keep this in mind, though:

1) You'll want your activated Behaviour to stick and not automatically 
change. Activate "Preferences > General > Advanced > Manually 
activated Behaviours stay.." to achieve this. 
2) You'll want to give your own Behaviour a different name, so you can 
differentiate the two. 
3) You may also want to make use of the items in "Actions > 
Behaviours" in the context menu configuration at "Preferences > 
Behaviours > Context Menu" to be able to easily go from one Behaviour 
to the other. Or, even more direct, use a button to assign such an 
action.

Other than that, if you need more buttons and you have Bluetooth in 
your Mac, I can recommend the BD Remote (see "Supported Hardware" on 
this website) for a cheap option to get a boatload of buttons on a 
single remote. Or, if you don't mind an external receiver, the Keyspan 
Remote for iTunes is also a very good choice (although with not as 
many buttons as the BD Remote).

Hope that helps.

Best regards, 
Felix