What would happen if B.caapi was ingested sublingually, then after a couple of minutes freebase DMT was vaped? Would the end result be like smoking changa? Also since the B.Cappi was ingested sublingually does that mean no special diet would be required?

No special diet is required in general anyway... the biggest risk is if you are on some other medicine or prescription drug like an SSRI anti-depressant. The food thing is a non-issue.

I would expect that waiting 20-40 minutes after taking the tincture might be more effective than waiting a few minutes. Still I have had aya experiences that worked quite well where the caapi and DMT were taken together at once in the more traditional manner with excellent results.