1. Unless you have documentation or confirmation from your vendor/manufacturer that the wig is “heat friendly” or “heat resistant” you risk melting the wig fibers. Modacrylic fiber is just one type of synthetic fiber. While it does have good heat-resistant properties you should test a few strands on the iron’s lowest setting first.
2. I have a human hair wig and want to straighten it out it. Most people suggested getting a curling iron that has a variable heat setting and keeps it on the lower settings to avoid burning the wig but I don’t know if the same applies to synthetic wigs. Try it out on one of the wigs that you can deem expendable for the name of science.