If you are concerned about the 'changa flu', you can always use another herb. Here you have a list
https://wiki.dmt-nexus.me/Changa. There are some herbs I wouldn't advise you to use such as brugmansia and heimia salicifolia.
But if you want the 'smoked ayahuasca' experience, well, you must use your caapi or other harmalas and see how your body reacts to it. After some tries, decide which is the best dose for you. As concombres said, take them separately and then figure out the proportion for your changa so that you don't waste caapi and spice.
About the changa flu, ayahuasca can make you have some flu-like symptoms especially in your first times, so start low and increase the dose in each experience. If you are afraid not to take enough (and scare in DMT land) or too much (and get the changa-flu), you can always take a low dose of caapi and add another herb so that you get neither scared nor ill.
I hope you found this helpful.