No. You must sand the gloss of and them prime and then paint. Semi and High Gloss is only meant for wood not dry wall. Its the worst idea ever to put a gloss on dry wall. Any paint with an Enamel is...
Yes as long as you use the same base paint. You just need to sand it enough to where the paint will adhere. Make sure if the original paint is latex, use latex. If its oil based, use oil based.