Would it be possible, and if so, useful to, say, use some citric acid whilst the freebase is in its extraction solution, in order to precipitate the pure DMT salt?

this is typically how DMT is retrieved from an aromatic solvent (especially limonene - which can't be evaporated), as they can't be freeze precipitated.

i do not know if there would a point to salt naphtha or other aliphatics - but i would think it would work.

typically after acid is added, water is added and agitated with the solvent to pull the salted DMT out of the solvent.

the water is then evaporated

Thank you Parshik. This was very helpful information