Yes of course we like answering questions as it helps us know what the crypto community is thinking!
Restaurant A would issue its own branded token. You would need to take this token to the GAT Exchange and sell it there for GAT Coin. You could then use this GAT Coin to buy tokens for Restaurant B (or hold them, or trade them on an external exchange)
You can see this process mapped out in our overview https://www.gatcoin.io/wp-content/uploads/2017/09/170928v2-GATCOIN-System-Overview.pdf
So pretty much the same way i can take current tokens/coins to any participating exchange, sell it and take the money to buy a different token/coin?
Why don't you just have an ICO for a new exchange? and pursue that angle.
The whole we part of a long list of companies that issues tokens but didn't really tweak any codes related to the aforementioned service has already been used up and won't be viable for long.