What is the halacha regarding using velcro (not heated) rollers to curl a sheitel on shabbos or yom tov?
The curling is quite weak and straightens out after about an hour.
Braiding or making up hair on Shabbos is generally prohibited because it resembles an act of building. However simple parting or brushing [when there is no concern of pulling out hairs] is permitted. If a shaitel is straight and curls are being made from anew, this would seem to fall under the above prohibition, even if it temporary in nature. However if the curls are already there and they are just being improved in a way that won’t last long, this would be permitted.