Is there any way to reduce the volume of extraction liquid after basifying? I feel like boiling a lye solution isn't a great idea.

Indeed no good idea.
Mister had once a too large volume for the usual recipient, an experimental spin off
He found himself forced to split the volume in 2, and do a double job of pulling.
Working, it did. Same yield.

Is re-acidifying again out of the question? (To evap in that state again.)
Mister never tried that one.

Thanks for the reply, Jees. I've followed a similar process in the past as far as splitting into multiple vessels. In this situation the goal is to combine 4-5 old jars of base soup that are sitting around to see if there are any goodies left. Just going to toss them if I can't get them in the same container, not worth the time...

How does one re-acidify basified liquid? Just add a metric ton of acid?

Yes, but I believe the technical term is "shit ton". This is much easier if you have some glacial acetic or citric acid as they are weak acids and won't increase your volume much.

I have done this once or twice by using hydrochloric acid, that is probably the strongest acid I can think of.

It also turned out I used a shit ton of lye in the original mix so it took about 1 liter of hydrochloric acid, haha! If you only used a smidgen of lye to basify then only a little bit of hcl will do the job. You will notice it when the color changes.

You could try to drop the temperature of the water to near-freezing point. Dmt freebase is just slight soluble in water at room temp, so it might cause the dmt and lye to at least create a second phase in the liquid, where you could then remove the top layer with a syringe to reduce the liquid.

EDIT: saturate the solution with NaCl to the mix before putting it into freezer, this will aid in the formation of the second phase at the bottom where the dmt will most likely to be fully present