Can I kasher a milchigs dishwasher to use for fleishigs?
Technically it is possible, however the custom is not to kasher anything for milchig to fleishig or vise versa because, by doing so things can get confusing what it is at this point milchig or fleishig.
There are times when one is allowed to kasher from one to the other, such as in extenuating circumstances. Or, if it is sold or given as a present to another; or if it was kashered to use for pareve, then, after a while it may be used for the other type. Others say that if the item wasn’t used for 12 months it may be kashered to the other type
Magen Avrohom 509-11, M”B 451-19, Pri Megadim E”A 452-13, Chasam Sofer Y:D 110, Beer Moshe 3-105, Maharsham 2-241