Sounds like maybe some ABA therapy. My sons have not gone through it but it basically sounds like classical conditioning. Teaching a new, appropriate behavior to replace a negative behavior. Sorry he's struggling. Hang in there!

I wish I could find the answer. My son went out for a walk and forgot to take a drink and pinched water from the shop the weekend. He told his sister about who told me. I sat him down and asked him if he could think of another way he could have handled it. We discussed phoning us to say he was thirsty and felt like stealing. Going into shop and asking if he could have bottle water and bring money back later, ask whether we could pay over the phone by card or whether he could just ask someone in the shop if they could give him a drink. We discussed ways of dealing with impulse as in, if he feels like stealing something from home be honest and communicate to
Is that he wants xy or z and that he has thought about stealing it. We have said he won’t get what he wants all the time but it might
Make us aware how often we say no
And we could explain why and offer alternatives. I don’t know if this will work but I’m out of ideas because consequences don’t do anything he just becomes more secretive

My daughter is 12. The sneaking food is terrible. It’s so frustrating. Yesterday she stole food from a girl at school. At least they believe she did. She lies so well, I don’t know what to believe. There’s enough “reasonable doubt” to wonder. I hate not knowing. I just wish she’d stop or at least be honest about it. I guess lying is a sign of remorse. We lock up cabinets with combo locks. Just know you’re not alone.