I haven't really had to do much tank swapping except on Ultima Hard Mode (haven't won yet, either) but what I do when I'm about to pick up is 1: make sure I'm in Shield Oath if I swapped to Sword Oath to add my pittance of dps. 2: start hitting Fast Blade while waiting on the third stack of the debuff to land, then 3: when the third stack lands, pop Provoke and follow it with the Savage Blade/Rage combo I've got myself set up for. Fast Blade isn't much aggro by itself, so I keep it before 'voke so my first 2 moves after it are high aggro.

Conversely, and this is probably a Bad Thing I need to not do, when I'm handing off to someone (I see them run over to me from the flank) I'll hit Z to put my weapon away and stop my auto attack so they're free and clear to pick up without me stealing it back. This is especially true if I'm better geared (atma weapon, so in DF I usually am.)