I simply want to thank the list and in particular, Christopher Browne, 
for your patience in assisting me with updating our replicated databases 
DDL.  This morning, I successfully added a field to a table on 12 
replicated databases.  It was still a relatively complex process as I 
had to reset the slony triggers on the master node once I updated the 
table via the 'execute script' mechanism.  The basic process was as such:

1. lock all users out of the database by modifying the pg_hba.conf file 
and restart the postmaster.
2. update the table via 'execute script'
3. reset the slony triggers to 'fire always'
4. allow user access by returning pg_hba.conf to it's original and 
restarting the postmaster.

Thanks again for all the input and patience of the list.

-- 
Until later, Geoffrey

Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety.
  - Benjamin Franklin