I want to make absolutely sure so here's what I planned: Infiltration (with Will as archetype; which Lupa already has the skill for) -> memory restoration -> Lupa acquires his own archetype (Branches) and takes that as a separate skill

Does that sound feasible to you, or would I have to put it off until post jaunt?

I can work with that. A struggling Champion going Pillar really fast and then getting helped back out of it. Actually can Pillars ever go back to being another role ever? I suppose that's the most important first question to ask. If the answer to the first question is yes, when a Pillar stops being a Pillar, can they potentially go back to Champion or Adversary?