RFMoore:
Maryland has some of the more strange sex offender laws in the nation. In most states only felons are required to register as sex offenders. You should fight this as hard as possible. You should petition the court that you were convicted in for a hearing on the merits of the state trying to make you register. I have seen one case in the past in which the person convicted in Maryland was in a very similar situation. He petitioned the court for a hearing on his status as a sex offender. The court ruled in his favor that he did not have to register. This individual actually represented himself, or was pro se.
Contact the court in which you were convicted and ask them about the procedure to petition the court about the status of you probation and the state attempting to make you register as a sex offender. If you can affored an attorney, you should hire one in the local area. If not, also inquire with the court to see if the court will appoint a public defender to take your case. Since your probation is being extending, the court should entertain giving you a public defender. In many jurisdictions courts will do this.
In summary, you need to fight this as hard as possible. As a registered offender, no matter where you go across the country, the likelihood of you having to re-register with the state or area is very high.
Lawyer
In House Counsel for Law Enforcement Agency