Basically the answer is yes but you are going to need a lot of new stuff and it is a lot of messing about. What reason do you have to want to change it ??
I should add that it's difficult to find 1 1/4 threadless parts. They're out there, but the options are minimal. If you're going threadless, you might want to get some headtube reducers to convert to a 1 1/8 setup.