Altering a CHAR(4) column CHAR(5) changing pg_attribute

I have a table with a column of type CHAR(4) and I want to change the
column type to CHAR(5). This table is referenced by many other tables
and dropping it and recreating will be a massacre...

So I have had this idea:
why do not change the row of that column in the pg_attribute system
table?

In particular my idea is to change the atttypmod from 8 to 9 (I have
thought char(5) is larger 1 byte than char(4)...then...).

Is this possible? There will be bad consequences for my table?
If anyone has any tip...

The related row is:

attrelid = 18865
attname = channel
atttypid = 1042
attdispersion = 0.0022182
attlen = -1
attnum = 7
attnelems = 0
attcacheoff = -1
atttypmod = 8
attbyval = f
attstorage = x
attisset = f
attalign = i
attnotnull = t
atthasdef = f

Thank to everyone for your replies...
--
Doct. Eng. Denis Gasparin: denis(at)edistar(dot)com
---------------------------
Programmer & System Administrator - Edistar srl