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As for switching to a different artifact and then playing evil Doms in the same phase, I'm not sure.
Ongoing Abilities > Protect Default ConditionsProtect abilities last until the end of the phase in which they are used.
That would be true if it weren't for the fact that you can have Gifts up from the previous turn, bring back Feast of Trumpets and draw off Gifts, then activate a different Artifact since you can perform prep phase actions in any order. It is possible and even common to use two Artifacts in a single turn.
I asked that same basic question long before I was an elder, except the cards involved were Feast of Trumpets and Gifts of the Magi. I wanted to bring FoT back, use Gifts for extra drawing, then change my Artifact. Much to my dismay, the ruling Bryon gave was that using the ability on Gifts during my prep phase was indicating that I chose that for my active Artifact for the next round, so I was not allowed to change it. I just did a quick search for that topic but apparently it's old enough to have been lost in "the great purge".I haven't seen or heard anything this would change that ruling so I believe it still stands. In the rare instance that you can force an opponent to use the protect ability from an Artifact during their prep phase, like in Pol's example with $4, base on the previous ruling by Bryon, I would say it's a clever way to keep someone from changing their Artifact for a turn.
Is the re-activating a deactivated artifact rule like the the unique characters under your control rule in that in can be done under no circumstances? Or could you deactivate your artifact (say lampstand) and then use a card like U&T or, during battle, Casting Lots or The Meal in Emmaus to reactivate that same artifact during that same turn?