You need more clicks to do that, I believe a modifier is the best way to do that;
#show [OFFHAND WEAPON]
/equipslot 17 [OFFHAND WEAPON]
/cast shiv
/equipslot [modifier:shift] 17 [DEFAULT OFFHAND WEAPON]
When you hold shift and click the macro it will equip your default off hand weapon.
I just went online to check, if you put it like '
#show [OFFHAND WEAPON]
/equipslot 17 [OFFHAND WEAPON]
/cast shiv
/equipslot 17 [DEFAULT OFFHAND WEAPON]
When you click it a second time you will cast shiv again, and equip your default OH wep.
That method works if you don't mind casting shiv twice, but as it is a waste, I'd rather use the modifier one, or a seperate macro to equip the old one. Depends on what you find easier
