Is there any easy way to paint over exterior painted woodwork that is cracking?

In a word, no. This cracking develops as the paint begins to lose flexibility and it no longer expands and contracts with the substrate. The more layers of paint, the worse the problem. Small areas of cracking can be treated by scraping and rubbing down. But large areas will need to be completely removed with a hot air gun or suitable chemical paint remover. Bare surfaces should be primed with an appropriate Weathershield Primer before painting.