Turning off Autovacuum

Not quite a performance question, but I can't seem to find a simple answer
to this. We're using 8.1.4 and the autovacuum daemon is running every 40
seconds cycling between 3 databases. What is the easiest way to disable the
autovacuumer for a minute or two, do some other work, then re-enable it? Do
I have to modify postgresql.conf and send a HUP signal to pick up the
changes?

I figured this would work but I can't find a reason why not:

# show autovacuum;
autovacuum
------------
on
(1 row)

# set autovacuum to off;
ERROR: parameter "autovacuum" cannot be changed now

In postgresql.conf:

autovacuum = on

Thanks,

Steve