will "alligator" or start to crack all over the place. Scraping is usually out of the question as it is quite a mess and you might have lead in there somewhere.
You can go to a paint store and get some spackle and a good flexible wide bladed putty knife. You can "float" the paint with the spackle. It is shrink free and with the spackle forced into all the cracks you might be there. I have done this on exterior paint under a porch that had large amounts of buildup. It worked pretty good.
Be sure to use a compound that is "shrink free" this will save you a re do step. Joint compound seems the logical choice, but it will shrink and you will need another coat after the 24 hours of drying.
You can also get a paint at a paint dealer that is heavy in bulk that is very thick and will also do the same result for you IF the cracks are not that deep. The product is actually a filler, its soo thick that I think you have to only brush it on.