plpgsql - Insert from a record variable?

Dear Postgresql experts,

I'm writing a simple plpgsql function that selects a row from a table, modifies it slightly, and inserts the modified version. This sounds simple, but I can't find how to do the insert in a simple generic fashion: although SELECT has a form that puts the result in a record variable, INSERT doesn't seem to have anything similar.

What I'd like to be able to write is something like this:

DECLARE
R RECORD;
BEGIN
SELECT * INTO R FROM TABLE WHERE id=n;
R.something := x;
INSERT INTO TABLE R;
END

But as far as I can see the only syntax that is allowed for INSERT is the normal INSERT INTO TABLE (x,y,z) VALUES (a,b,c). To achieve what I want to do I'd need to iterate over the fields of the record (how?) and build up the string of the INSERT query.

It seems odd that SELECT can use a record variable but INSERT can't, so I wonder if I have missed something. Any suggestions?

Thanks in advance for any help anyone can offer.

Regards,

--Phil.