I have used low doses of syrian rue extracts on the same day as ketamine and felt fine.. I am not saying there wont be problems with higher harmala doses but I think something like changa won't cause major interaction with ketamine.
Ketamine and harmala alkaloids have a very different mode of action and, as far as I know it, also quite different metabolic pathways.
It would be a different story with MXE as it is a serotonin reuptake inhibitor and that could cause serotonin syndrome if combinened in high enough doses with MAOIs like harmalas.
