What kind of work do you do? If you are on a 12 month probation order then do your work know about that from previous CRB checks?
I'd say you have to not only show you are making the effort to put a stop to the shoplifting but do it for yourself, if it's just a facesaving exercise then it will just happen all over again.
I'm sure the court services are used to people promising the earth to get out of a harsher punishment so whatever it is needs to be properly planned and actioned.
Be honest, seek proper advice, accept suggestions, show you mean it.
Could you also offer to do some kind of community work and put something back into the community?
Can you speak to your probation officer about the probably consequences, best course of action and get their help to put something in place and how to approach the court etc...?
Speak to your probation officer about the best way to approach your workplace. I'd say honesty is the best policy if it is going to come up anyway, rather than waiting until it is discovered and adding an additional deceit to the issue.