D.C. Mun. Regs. tit. 3, § 517
517.1 Prior to the thirtieth (30th) day preceding a primary election, a registered voter may give notice of change of party affiliation by:
(a) Completing a change of party on a Voter Registration Application;
(b) Filing a change of party by signed letter or postal card which includes the following information;
(i) The voter's name;
(ii) Former and new political party affiliation;
(iii) Address; and
(iv) Date of birth.
(c) Filing a change of political party through the DMV or a voter registration agency pursuant to D.C. Code § 1-1001.07(d) (2006 Repl.); or
(d) Completing any other form prescribed for this purpose by the Board.
517.2 The effective date of any declaration of party or change of party affiliation shall be the date that the notice is considered to be received by the Board; except that, no declaration of political party or change of party affiliation shall be effective if postmarked or considered received during the thirty (30) day period that immediately precedes any election. Requests for changes to a political party affiliation considered received during the thirty (30) days that immediately precede and include the date of the primary election shall be held and processed after the election.
SOURCE: Final Rulemaking published at 43 D.C. Reg. 1078, 1091-92 (March 1, 1996); as amended by Final Rulemaking published at 57 D.C. Reg. 3267, 3286 (April 16, 2010).