Getting off at an international hidden city with checked bags? [duplicate]

Most if not all airlines follow the same rules, if you don’t use one part of the ticket all subsequent legs on the same booking are cancelled, so whatever you do you need to make arrangements before hand

1) make sure I can get off in B and not be charged a lot of money/sued

Not really. If you do this you are violating the terms of conditions you agreed to when buying the ticket. The airline can come after you and in some cases sued. However, it's very unlikely that they would do this, especially if you are a first time offender. You made a mistake by calling them and asking about this. If the agent made a note on your ticket, it's way more likely they would be on the look out for intentional leg skipping.

2) retrieve my luggage at B or even be able to have someone pick it up at C for me, and

Unlikely. The airline will typically not short check unless you have a good reason, so you have to come up with a good story that doesn't smell like leg skipping. Since you already called them, they may have flagged your ticket already.

Chances are your bag will stay in B anyway. If you don't show for the B->C, they will remove your bag from the aircraft for security reasons. You may be able to retrieve it in B, but expect to pay a lot of money. Removing a bag from an airplane that's ready to go creates a LOT of operational extra cost and you will be charged for that plus some more penaltys and fees.

Even if your bag gets to C, it would be very hard to retrieve by a third party. If B->C is an international flight the baggage claim in C is in a protected area before customs. It would be hard for anyone to get in there to grab your bags in C. They would have to arrive on an international flight roughly at the same time. Depends a bit on the layout of the specific airport. If a third party can get in, they can just grab your bag from the carousel and walk out with it (through customs). Checking baggage tags is extremely rare.

3) ideally just move the second leg of my trip back so I don't have to pay tons of money.

That's exactly the reason why the airlines are so strict about this: they want you to pay tons of money and hold a you hostage around this. Buying an extra one way from the smae airline makes no sense. You can try to change the return date on the existing ticket but if that doesn't allow a stopover (which B is), than this be expensive. You can also try to just have change end in B. This may or may not be cheaper. Chances are, your cheapest option would be to fly it as booked and then grab a cheap return ticket C->B->C on the day you arrive. At this point you can also squeeze in an extra day in C to get showered up and repack your bags (assuming that's home for you)