resizing a varchar column on 8.3.8

Hi,

I found a post with some instructions for resizing without locking up the
table, but would like to get some re-assurance that this is the best way:

http://sniptools.com/databases/resize-a-column-in-a-postgresql-table-without-changing-data

How does that affect data storage and future updates on existing rows?

The table has around 6MM rows and is very heavily queried. I'm also using
skytools londiste for replication, so I assume that I would run the resize
on the subscriber first.

Thanks for help,

Jon