Changing pg_attribute.attislocal

Over time, I mistakenly did something like this:

CREATE TABLE a ();
CREATE TABLE b () INHERITS(a);
ALTER TABLE b ADD col int;
ALTER TABLE a ADD col int;

where I should have left out the third statement.  Not a great loss, the only
consequence I've observed being pg_attribute.attislocal = true, so dropping
a.col will not drop b.col.  Is there a DDL way to change that, short of dropping
the column from both tables and re-adding it to the parent alone?  If not,
what's the danger of updating attislocal directly?  If it makes any difference,
I don't actually plan to drop the column anytime soon.

Thanks,
nm