If you want to prosecute someone who has previously been pardoned, then you'll have to figure out how to get the courts (that is, the people who would be doing the actual prosecuting) to ignore some of the highest rules by which they operate.

I'm not saying that that could never happen, but a) it sure sounds like an uphill battle and b) it's not the same thing as the president (one person) doing whatever they feel like regardless of the law.