This is off topic, but... when the blocksize changes, the blockchain will fork, right? What happens to bitcoins 'in' wallets that are represented in the 'old' blockchain? Do they have to be coverted/sent to the new blockchain at some point?
When the blockchain forks, anything before the fork is in both chains, so nothing is lost.
To see why, think about this at a much coarser granularity: just people who operate miners. Suppose a new version of the BitCoin software comes out which makes you lose all of your money. Will you switch over to that software? No, you'll just keep the old version that lets you keep your money. What about the peer pressure to switch over? Well, if all of the peers stand to lose by switching over, your peers are likely going to band with you, precisely to not switch over.
Therefore any change needs to be backwards-compatible. Software changes come in the form of updates, "Before block #123456, block sizes will be X; for that block and after, block sizes will be Y," issued some months before block #123456 is likely to show up.
It's actually a parallel to something where I saw an agnostic philosopher debating some Christian fundamentalists who were totally out-of-their-league. They were supporting a divine-command-theory of morality. He was saying something like, "That's stupid: your morality could change tomorrow; God could tell you something different, like that you have to kill babies, and then that would become the Right Thing to Do -- but that's in the face of every moral intuition we have."
They were saying something like, "of course, God can't change his mind because he's eternal, so that's a non-issue. The laws of morality are therefore eternal and your example is impossible."
He replied, "No, I'm saying that God's eternal rule could be, 'Before 6AM on May 15th, 2016, GMT, killing babies shall be bad, and afterwards, it shall be everyone's duty.' It's a perfectly eternal rule that does not require God to ever change His mind. And you're saying that you're totally comfortable if that turns out to be the way that God's moral laws work, right?"
To a temporal agent, an agreement about the structure of eternity can always be renegotiated among those agreements which amongst themselves agree on the past and nearby future.