Creating simple type aliases

Is it possible to create an alias for an existing type, so that I can refer to
it with a simple name, and possibly change it in the future? Something like:

create type-alias issn as char(9)

Without that it looks like I have to do

create type issn (
input=charin, output=charout,
internallength=9, externallength=9,
element='char'
)
then insert a row to pg_opclass, after attempting to use the new type to find
its ID.

Surely there's an easier way?

--
Peter Haworth pmh(at)edison(dot)ioppublishing(dot)com
"Never tell people how to do things.
Tell them WHAT to do and they will surprise you with their ingenuity."
-- Gen. George S. Patton, Jr.