reply to dinofelis, without the long quote, lol
so........say i hard forked BTC and changed nothing but the merk. now i have a new coin with the same name and abbrev as Bitcoin. if i compiled the standard QT wallet, i would, in appearance be dealing in BTC, but actually dealing in my own coin. even though my wallet would have an address that matches the proto of Bitcoin, any transaction sent from that wallet would be rejected by the block chain as invalid because it comes from a different chain, my blockchain would be different from the one accepted by the rest of the network. but what about nodes? if i spread my bitcoind as the real one, and others use it, but try with the standard set of nodes, plus with my node added, would each wallet be a loner, outcast by the network, or would the few wallets of my coin find each other and grow the block chain that i created?
You can of course not do this unnoticed :-)
I have the impression that you are somewhat confused about certain notions in crypto, or else I don't understand your questions.
In a certain way, you should see a coin as an object (in computer science) of which the data (attributes) is the block chain, and the software (methods) is the node/wallet software. The methods implement a protocol (essentially what is described in a white paper) and attach to a genesis block. There can of course be many different implementations of the protocol, but as long as they are compatible, it doesn't matter, they agree on the protocol, and they agree on the block chain.
A hard fork consists in writing a new set of methods, such that the protocol has changed, but the genesis block and the "genesis chain" (that is, the chain up to the fork) is identical. You can say that the "genesis block" of a fork is the last common block of the original chain, but there is much more: the forked methods still accept the old protocol BEFORE the fork, and so all old addresses, with the old transaction protocol.
As such, from that point on, a new block chain is created which has, in principle, nothing to do any more with whatever happens on the prong after the split on the old chain. Most conceptions of "hard fork" were in fact that that old prong wouldn't exist. The surprise of the ETH/ETC split is that the old chain lived on.
In order for a chain to exist, in order for it to get new blocks, there must be miners on that chain. One single miner is a priori sufficient, if difficulty adapts quickly enough (which is not the case on the old bitcoin protocol btw).
So as long as:
1) you have written new methods (new node software)
2) there is at least one miner building blocks on your chain
then your new currency lives on. All people having unspend coins on the old chain are automatically in possession of the new coin too (even if they spend their coins on the continuation of the old chain after split).
I don't understand what you call "changing nothing but the merk.". In order to have a hard fork, you have to have different, incompatible software running on the nodes (and hence on the wallets which are part of the nodes). You can, by definition, not have a hard fork with the same node/wallet software.
People will of course notice that the node software is different. The idea is not that this gets by unnoticed.
The ETC/ETH split was a funny split because, apart from some if statements concerning the DAO, nothing changed in fact. But you could fork from, say, Bitcoin, and make a totally different protocol, with different mining hash functions, different rewards (for instance, no halving, or a different emission scheme). The only thing that your software needs to implement, is all the old bitcoin protocol aspects concerning everything BEFORE the fork, and needs to implement a way of handling transactions from the old chain to new addresses (which can be totally different too if you want to).
There are miriads of possibilities that have opened up, and the concept of block chain has changed into "block graph". If only forks occur, then what used to be block chains, will become "block trees". But in fact, nothing stops now from MERGING old chains, and accepting old blocks from two different chains, into a new one. That would then be a "block graph".
The linear chain has changed into a tree, and potentially even in a general graph.