Much of the point of starlifting is likely gonna be to extend stellar lifetime anyway, right? Any materials coming up "the fountain of youth" in excess can simply be dropped back into the star to maintain desired opacity.
Tuning metallicity might allow us to shrink down to a red dwarf with an unnatural spectrum, though! What that spectrum looks like depends on what we look like, so speculation on that is another topic altogether, but maybe a good guess is that our preferred spectrum will be what's easiest to harvest technologically, just since a red dwarf-scale lifetime is an improbably long time for us to keep running around in meat bodies. Maybe we'll end up wanting bluer light if the longer gradient down to waste heat is better, or maybe we'll get efficient enough to slow down and sip energy from brown dwarves for an even longer lifespan, or maybe both of those at different times and a lot of steps in between.
Ook, speaking of that, a Dyson swarm over such a span is a lot of time and space for diversity to develop! It's conceivable our descendants will diverge enough that it makes sense to run two dwarves with different chemistries, though now we think of it, that does sound like it might be a lot of gravitational potential to spend energy on.