We were at Disney last week and saw that tactic not allowed at Le Cellier. Some people with 2 adults on the dining plan wanted to get 4 adult meals. The guests made a big fuss and ended up being embarrassed in the end. One of the managers told them those were the rules at his restaurant and they may be happier somewhere else. They huffed and puffed, but they stayed and paid cash.
Like everything Disney, enforcement is spotty at best, and you could well go to Le Cellier on the same night and be successful.
If you have 2 Adults on the plan and want to share 1 TS, you should have no problem at all doing that.