In Maryland can an heir to an interest in real property assign that interest to another person?

Yes. The heir can "disclaim" the interest before it is distributed and it would serve to increase the relative interests of the other heirs. Or, the heir can receive the interest (a deed from the estate) and then sell/assign to others by passing another deed.

If you have a legitimate interest in property then you have the right to assign your rights to that interest to another person. If your interest is a contingent interest, meaning that some event has to occur before your right matures, then the assignment of your interest will be subject to the same condition precedent. So, in short, you can make an assignment of your rights to an interest in property but the interest may be subject to conditions that have to occur before the assignment can be enforced.