No, what you mean to say as long as your modified software adheres to the rules of the protocol set by the developers of Bitcoin-Qt/Bitcoind after they push a protocol change that is approved by Gavin Andresen, who has the final say. Ask him. He wants to be the Linus Torvalds of Bitcoin. He wants the approval process of Bitcoin changes to be just like Linux.

If the majority of the network accepts Bitcoin-Qt/Bitcoind protocol changes under Mr. Andresen's guidance, your modification will mean squat. It will fork and you will be left with your toy Bitcoin that nobody accepts.