Advance Standing Transfer from D.O. programs

I'm sure it has happened at some point into some school, but this is exceptionally rare (and and usually occurs after the 2nd year and successful completion of the boards). This requires approval from both schools and there must be an open spot in the class you're trying to transfer into.

One needs generally a good reason for transferring such as being closer to a spouse that has been transferred or a sick family member.

Wanting to be a MD over a DO would likely not be a sufficient reason.