Md. Code, Election Law § 3-303

(a) Notification of a change of party affiliation or a change to or from a decline may be made:

(1) by information provided on a voter registration application by the same methods provided for registration under Subtitle 2 of this title;

(2) by written notice, signed by the voter and sent by mail or otherwise delivered to the local board in the county where the voter’s current voter registration address is located or to which the voter has moved;

(3) by making application in person at the office of the local board in the county where the voter’s current voter registration address is located or to which the voter has moved;

(4) by information on a voter authority card or other appropriate form filled out in a polling place; or

(5) by changing a name or address with the Motor Vehicle Administration.

(b) Party affiliation changes or changes to or from a decline:

(1) shall be processed at any time that registration is open; and

(2) except as provided in subsection (c) of this section, may not be processed when registration is closed.

(c) If a local board receives a request for a party affiliation change after the close of registration, the local board shall make the change and it shall become effective for the next election provided:

(1) there is sufficient evidence, as determined by the local boards pursuant to regulations adopted by the State Board, that the request was mailed on or before the close of registration for that election; or

(2) the request was submitted by the voter to the Motor Vehicle Administration, a voter registration agency, another local board, or the State Board on or before the close of registration for that election.