Altering the blockchain

[Hindsight]

Is there any possible theoretic way to alter the blockchain of bitcoin? Or is it possible to create an own address where you can choose your own characters? Is it also possible to send unconfirmed bitcoins? I guess the answers to these questions are no, but wouldn't there be a theoretical way to do this?

[Akka]

Is there any possible theoretic way to alter the blockchain of bitcoin?

Only of you get enough Nodes to agree with your alteration. F.E. if you have more Calculation Power as the combined rest of the Network and the alteration doesn't violate any protocol rules.

Or is it possible to create an own address where you can choose your own characters?

Adresses are created out of your private keys and there is no way to know how it will look before.

But you can create vanity addresses simply by trying often enough, there are programs for this like vantigen (see the Address in my sig.).

But the time needed grows exponentially with each additional character.

Is it also possible to send unconfirmed bitcoins?

Yes, this is indeed possible, not with the standard client, though.

And any unconfirmed coins you send, will of course not confirm before the Transaction that you received the coins with has confirmed.

[Hindsight]

Thanks for the reply Akka. I have found a way to generate as much unconfirmed bitcoins as I want. Now I only need to find out how I can transfer those unconfirmed bitcoins to 'real' bitcoins. Does someone have an idea? How high are my changes to achieve this? All help is welcome.

[Akka]

Thanks for the reply Akka. I have found a way to generate as much unconfirmed bitcoins as I want. Now I only need to found out how I can transfer those unconfirmed bitcoins to 'real' bitcoins. Anyone has any idea? How high are my changes to achieve this? All help is welcome.

Your chances are about 0%. Sorry. The network will only accept coins that come from an unspent output. You may be able to chance your local client to "create" more coins. But other node wont even rely them as it is a violation of protocol rules.