You can add custom xprofile Fields in Users > Profile Fields (BuddyPress extended profiles must be enabled). Once created you can the read and write them from code

Read an xprofile field

$MyString = xprofile_get_field_data( 'UserType', bp_loggedin_user_id(), $format = 'array' );

Write an xprofile field

xprofile_set_field_data('UserType', bp_loggedin_user_id(), $MyString);