Peter Geoghegan wrote:
> 2. If it is sensible, is it possible to achieve the same result
> through calls to "bare metal" slony functions?

I don't know any officially approved way of doing this, but you could disable the user account slony is using to connect 
to the database and terminate any existing connections, like this:

-- prevent user slony from logging in
ALTER USER slony NOLOGIN;

-- terminate all connections for user slony
SELECT pg_terminate_backend(procpid)
FROM pg_stat_activity
WHERE usename = 'slony';

-- your changes here
INSERT ....

-- allow user slony to log in again
ALTER USER slony LOGIN;

After a minute or so, slony should reconnect to your database and begin replicating the changes.

Regards,
Aleksander