Altering a table with a rowtype column

Given a pair of tables:

create table a (
id serial,
stuff text,
more_stuff text
);

create table a_audit (
id serial,
old_record a,
new_record a
);

How can one alter the structure of table a? Attempting

ALTER TABLE a ADD COLUMN even_more_stuff text;

results in the message:

ERROR: cannot alter table "a" because column "a_audit.new_record" uses
its row type

A solution that doesn't lose the existing data is preferable.

Mike