Macro help please :^)

So I’m trying to make a macro that uses this offhand item (5 min cooldown)
/use Skull of Impending Doom
Then on pressing the macro again it changes the offhand
/equip Fire Runed Grimoire

Kind of like cast sequence but they aren’t spells so not sure if possible

You could do the swap using /equipslot and specifying a bag slot but because they’re both Held In Off-hand I’m not sure of a way to automatically differentiate them from each other to make the decision whether to use or swap.
https://wowwiki.fandom.com/wiki/MACRO_equipslot

If it was me I’d set it up so that either the swap or the use was on a modded press and the other function not.

#showtooltip
/equipslot [mod] 17 BagSlotID
/use [nomod] 17