Yes, you can accept and then renege if required.
You should look at the terms of both your TC and VS offer to see if there are any terms that would stop you from doing the VS if you have accepted the TC. Depending on what they say, you might need to disclose to either or both firms.
Generally though, if there are no terms in either offer, you won't need to disclose it as you are not an employee of the TC firm until the contract starts.