I can see nmt forming a beta-carboline given the right conditions, that's a pretty neat idea. Though, the idea of mono de-methylation of the tertiary amine in n,n-dmt from boiling in water seems far-fetched especially in a water soluble salt form.
Totally true that different beta-carbolines will have different effects, especially with the DMT experience continually pressing novelty. An example being; THH does not interfere with GABA in a animal model(IIRC) while harmine and harmaline do. In this case I would expect the variance of beta-carbolines not to be formed from the boiling/brewing but rather in the plants themselves. Caapi has how many alkaloids in it? I recall a paper saying they found I believe 43, on-top of however many were already known and some perhaps yet to be discovered. Burnt's analysis on jungle spice if I remember correctly also depicted beta-carbolines or maybe THBC's I forget. So there is a vast area for incalculable variables involving plant brews from the DMT source plant as well as the MAOI source plant, on-top of any admixture.
As far as staying on topic though, I am failing to do so.