If you do the extraction yourself and have the crystals, I imagine it would be fine to smoke/vaporize. I've noticed that many people seem to get sick from changa. It's only certain people for seemingly unknown reasons other than they used IPA (isopropyl alcohol) for infusing their changa instead of acetone. For some reason, it seems like some are more suceptible to negative physical reactions than others because I've read a handful of reports with groups of people smoking the same dose of the same batch, but usually only the person who has gotten sick before gets sick. Smoking the freebase crystalline spice may be initially harsh (like for the first 3 seconds you hold it in), but after that you usually can't tell you're holding anything in at all (at least for me). If you're still having trouble due to your respiratory system (and believe me, I can relate - my lungs have gotten in my way of powerful experiences all too many times), you can always make pharmahuasca with your extracted DMT. This involves the use of an MAOI (syrian rue and caapi are the most popular and effective for these purposes) as well as your crystal spice. Personally when I take pharma, I usually use 3-4g ground up syrian rue which I stuff in gel caps and poke some holes in with a thumb tac. Next, most people prefer to convert the DMT into a salt form to reduce nausea. This can be as simple as dissolving it in OJ, or you can get fumaric acid and do a FASA to get DMT-Fumarate. In any case, I prefer to take the MAOI filled gel caps, wait 20 min and then take the DMT dissolved in OJ. It's always wise to dose low on the DMT end because these situations can get out of hand if you're not prepared to deal with them. Some people are simply more sensitive to pharma than others. I would start with 30mg and work my way up. Always better to aim low, and then you can smoke some freebase later on for a boost in intensity if needed.
"Science without religion is lame. Religion without science is blind" - Albert Einstein
"The Mighty One appears, the horizon shines. Atum appears on the smell of his censing, the Sunshine- god has risen in the sky, the Mansion of the pyramidion is in joy and all its inmates are assembled, a voice calls out within the shrine, shouting reverberates around the Netherworld." - Egyptian Book of the Dead
"Man fears time, but time fears the Pyramids" - 9th century Arab proverb