I use MOVE MEDIA for this operation both ways, out and in the library.
With CHECKOUT  you have to provide the volume labels of the tapes you want
to remove from the library, while with "move media" you can select by
stgpool. I am not sure if the "checkout" changes the access to offsite but
"Move media" creates a file with the volume label of the tapes that
processes, and you can afterwards run a command to perform an update of the
volumes with access=offsite.
The only problem is that, what the command creates is a macro and can only
be scheduled by a cron job,( my system is UNIX.)
The macro can not be scheduled by TSM, not included in a script. It has to
run from the command line.
Regards
Maria