Here's a crazy idea: put each little block of code in its own file. So, create a file with this content:

#!/bin/sh
/usr/bin/su - patrol /usr/adm/best1_default/bgs/scripts/best1collect -
+q >> $1 2>&1
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and name it 'start-bgs' in some directory. Then do the same for all other other case blocks and name them similarly. Then your script just becomes:

#!/bin/sh
...
# set $agent to the agent you want to start
cmdpath=$cmd_dir/start-$agent
if ! -x $cmdpath; then
    echo Error - start script $cmdpath not found
    exit 1
fi
$cmdpath $LOG # pass any relevant parameters here
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Then when you need to add/change/delete agents you are just replacing files instead of trying to edit a few lines in a file. This should make things a lot easier to manage, especially if you have several hundred files to update.

It's a crazy idea!