Can u mix a semi permanent hair color with a color booster, like a powder bleach?

No. The chemicals will not mix well. If they even do mix, there's no telling what color you will get. You can mix a higher volume creme developer(peroxide) to a light color and lighten hair color without bleach. I use Clairol, Beautiful Blondes, 12B, 1 Blondest Beige. One part color (one ounce) to double developer (Peroxide) For no longer than 35 minutes. Usually under the dryer with a plastic cap on, to help lifting. This is how I highlight my hair, after pulling through a plastic cap made for highlighting. I use 40 Volume Creme Developer. This application is a lot easier on your hair than bleach.Can u mix a semi permanent hair color with a color booster, like a powder bleach?
you can, but the bleach will be permanent and make it harder to get the semi permanent color out.