USB Overdrive how to use a modifier key to change the macro executed

On my Mac I use USB Overdrive to assign the macros CmdShift[ or ] to switch tabs quickly with my mouse's side buttons. I wanted to know if it was possible to make it so that when I am holding down a certain key e.g. Shift and then press these side buttons I can have it execute a different macro than when Shift isn't held down? Basically, I want to be able to use the side buttons to either switch between tabs or go forward/backward depending on if I'm holding down Shift.