Also, is it possible to change the reward cycle duration or the number of mining- reward coins?
1 Answer
Technically, yes, yes, and yes. However, I'm not sure if we'd still call it "Bitcoin" at that point.
Any of these changes would require a hard fork, which means that the underlying rules of the system are changing in a non-backwards-compatible way. It means that blocks/transactions from after the fork are not guaranteed to be considered valid to nodes running software for pre-fork.
So, to change Bitcoin like this in practice would require convincing the entire rest of the world to agree with the changes. Anything less, and you will end up with two versions: the original and the one with your changes. Which one gets the title "Bitcoin"? I don't know. That's a non-technical question, and a point of contention.
For an example of this in practice, see Bitcoin Cash.
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that means : change is possible technically, but it required to be soft-fork nor it will cause a new hard-fork . thank you for your clear answer. my question was because i have thought about what bitcoin situation will be if its price decreased to a low levels for long years from now and may its mining rewards will become uneconomic .so there are many solutions to avoid that .– H AkhaliCommented Dec 14, 2018 at 21:38