Can BTC and BTClike transactions be returned to sender or rejected?

[daftmythic]

I am curious if it is possible (either inherently in the BTC client or established protocol, or theoretically by examining the blockchain) for an arbitrary transaction received into a wallet to be returned unchanged (or maybe minus transaction fees) to the source? If so how?

not as critical but since I am on the topic: can an incoming address be "blocked" so it cannot send you any more coin. Alternatively, can a receiving address be "turned off" so that it will block/return any transactions that are attempted to be sent to it?

I am asking because I had an idea for a alt-currency service, but having the ability to arbitrarily return coins from certain sources would be helpful. Something like coin escrow.

[zekesonxx]

A receiving address can be ignored, so any BTC sent to it will be in the void. With payment services they usually reuse addresses or just pocket any extra.

You can just send money back, but there is no way to "reject" a payment. Well it is technically possible, but it would be pointless.

There are a bunch of bitcoin escrow services.