SQL would be the fastest way to do that. Example as follows.
Code:
UPDATE `jos_comprofiler` SET `FIELD_NAME` = 'OPTION_Z' WHERE `FIELD_NAME` IN ( 'OPTION_X', 'OPTION_Y' )
Change jos_ to whatever your database table prefix is and be sure to replace FIELD_NAME, OPTION_Z, OPTION_X, and OPTION_Y as needed. Please always make a backup before directly altering the database encase something goes wrong.