I don't believe there has been a change in the rules recently. If he hasn't transferred from a 4 year school before, and meets basic academic and character requirements, any player at a 4 year school (D1, D2, D3, NAIA, or unaffliatated) may transfer to a D2 or D3 institution without serving a year in residence.
A baseball player who wishes to transfer to a D1 school typically does have to serve a year in residence before being eligible to compete. However, there is an exception that may apply to players who have received no athletic money and who were not recruited to their first school. I suspect this is not a common scenario, because most players who feel that they can realistically play at a D1 will have been recruited to a D3.