Note that you can't actually chain multiple attacks or powers together, it usually executes the first or last one in the list that can be activated (I forget which one it pics). However, if the weapons have long enough cooldowns then it works since it runs the first or last command that is allowable.
The only reason I mention it is say if you tried to have 1 button chain 8 beam weapons in series, you'd probably end up jumping back to the 1st one earlier than you'd expect since the cooldown would expire before you got to the 8th weapon.
You can chain emotes or targeting commands, like this fine, just not multiple attacks:
/bind Button4 "Target_Enemy_Next_Exposed$$+TrayExecByTray 0 1$$target_Clear"
That selects the first exposed enemy viewable, fires your exploit attack, then clears the targetting selection.