There are ways to do what the OP asked (for the most part). I know it's not the same as activating it all at once as you would like, but just as a continuation of what you already touch upon, you can spam the stuff to make it work.
/macro set # Change to "#" macro page (wiki calls it line?)
/macro book # Change to macro book "#"
You have several macro "pages" in each "book". You can use macro page 1, and set, (for example) cntrl + 1 to do
/equip "funny monkey hat"
/macro set 2
and then in page 2 of that macro book, you would set, again for cntrl + 1
/equip "Hat of 1000 truths"
/macro set 1
This would create a single "Macro Key Set" you can spam to toggle back and forth by spamming cntrl+1
(Just make sure you either duplicate all of the other page-1 macros to page-2 or you'll end up hitting them and nothing will happen. Alternatively you could just put /macro set 1 in all of the empty macro slots and be prepared to hit them twice.)
... That being said, I and everyone who plays FFXI on PC would regularly would probably recommend spending a day getting familiar with the XML of spell-cast (start from someone's pre-made sample for your class if you are not someone who codes at all, and you'll figure out where to cut out the parts you don't like and type in the gear you have). It allows you to swap gear "automagically" whenever you cast an appropriate spell. For example, you could have it equip WS gear when using a weaponskill, or the appropriate elemental stave when casting a spell that benefits from an elemental affinity.
Spell cast WILL do what you want, it has a 'before' and 'after' cast command, so the gear can be automatically 'reverted' to your TP or MP generation sets between ability uses.
(edit: it's been a while since I played, I may have messed up book and set, really can't remember which is which so if one doesn't work try the other).
Edited, Jul 1st 2013 6:36pm by FUJILIVES