Just switch your client to report values in mBTC. Done.
Hey I am selling this steam game for 2,000 mBTC. Anyone want it?
To change the value of Bitcoin would require increasing the supply (i.e. turn every BTC into 10 BTC). That is simply never going to happen. Not today, not next year, not ever. While in theory it "could" happen (any change could be made to Bitcoin with enough of a consensus) you will never find the consensus necessary.
Eh, I'll have to disagree with you on this one.
Transactions are done in Satoshi's (or whatever you want to call them). When I send a single Bitcoin to another person, I am sending 100,000,000 Satoshi's behind the scenes. A single Bitcoin is only a single Bitcoin because everyone agrees that's what 100,000,000 Satoshi's are called. If people agreed to 100,000 Satoshi's being called a Bitcoin instead, then the clients could be changed to show balances in the new denomination, and everything goes on as normal. There's no change necessary to the protocol itself, and no need to make 1 Bitcoin = 10 Bitcoins - it's all about how it is displayed to the end user.