Yes.
In particular, I use the CLI client. Here is a snippet from one of my scripts:
JOBFLOW_ID=`elastic-mapreduce --create --alive --name cluster --num-instances $
COUNT --hadoop-version 0.20.205 --ami-version 2.0 --plain-output --debug --log-uri $LOG_
URI`
echo "Launched --jobflow $JOBFLOW_ID"
elastic-mapreduce -j $JOBFLOW_ID --ssh
You could terminate with -j --term, issue cli commands to the master using --ssh. There is even a page in the DevGuide (which you should really read it) about adding more than 256 steps (done on a already launched instance, mind that), so its really not a huge concern.
