UPDATED 21/12/09 (Patch 3.3)
Patch 3.3 has broken the 'Safe' Libram swap macro at the bottom of this page, I believe as a sideffect of the breaking of Rogue poison-weapon swapping macro's. The less complicated one (listed first) still works, with the added benefit of having the character space to fit in calls to the Clcret rotation helper addon. Still, make sure you don't hit it accidentally.
If you are a Ret Paladin and have been involved in any sort of raiding content recently you should now be getting used to Seal Switching depending on the encounter or phase in a particular fight. You should also be using the Libram of Valiance, the super-sexy Relic deisnged for Seal of Vengeance. However I know that some of you aren't swapping their Relic along with their Seal, even though Valiance doesn't help SoCommand at all. Tut Tut...
Aren't you glad I'm here to help ;).
Libram swapping can be performed at any time, even during a GCD, but invokes a 1.5 second GCD. Hence if you Libram-swap as soon as you cast an instant you will only incur a total 1.5sec GCD, along with the usual reset of the weapon swing timer. The total procedure can be placed in a macro, seen below:
#showtooltip Seal of Command
/cast Seal of Command
/equip Deadly Gladiator's Libram of Fortitude
However, the Libram will still be swapped even if Seal of Command isn't cast. Correcting for this failure mode is a little tricky, but the following /run command should work out:
/cast Seal of Command
/run local f=RbA or CreateFrame("Frame","RbA") f:SetScript("OnEvent",function(s,e,u,p) if u=="player" and p=="Seal of Command" then EquipItemByName(42852) end end) f:RegisterEvent("UNIT_SPELLCAST_SUCCEEDED")
The script basically attempts to cast Seal of Command, and then if successful runs the EquipItemByName function with the arguement (42852). This number is actually the item number of the Deadly Gladiator's Libram of Fortitude, but you can input the item ID of any suitable Libram. In theory EquipItemByName can take the item name aswell as the number as an arguement, but in this case that option would take the macro over the character limit.
Check out Wowhead for ItemID's, the same number used in their item weblinks.
thanks to Glutton on the EJ Forums for this info