Want to upgrade your full node from BCore chain to the Bitcoin Cash chain? Instructions inside

As the Bitcoin Cash chain is maturing and we are getting more and more excited voices about it, I expect people that currently run full nodes may want to switch to run Bitcoin Cash instead.

Cash has from the beginning had 4 full node implementations, Xt, Unlimited, ABC and Classic. You can choose any one to be compliant with Cash. I am going to tell you that the best option here is Bitcoin Classic for your full node. For real reasons.

A unique feature in Classic is that it can take an already downloaded full-node chain and even now, some weeks later, convert it to a Cash chain with no repeated downloads.
This means that people running Core or other full node implementations can download the Classic UAHF version and regard it as a drop-in replacement.

But Classic doesn't delete or even touch the files on the 'Core' chain, so you can now run two versions as the same time where one shows BCCs and the other shows BTCs.

Here are the short instructions

1. Download Bitcoin Classic UAHF.
2. Shut down all Bitcoin nodes on your machine.
3. Start the new Classic UAHF.
4. Edit your legacy config file to stop your legacy node from 'listening' on the network. Find your config file (how?), open or create a bitcoin.conf text file there with the single line listen=0.
5. Start your legacy Bitcoin client again and enjoy being on two networks at the same time.

Have fun!

Boring explanation of what Classic does (feel free to stop reading here)

Classic creates a new directory BitcoinCash and copies only the required files there.
In the BitcoinCash dir you now have a new bitcoin.conf and the UTXO lives there which is completely separated from the old one.
The historical files (the 120GB of blocks) are not copied, we simply note down in the new config file where we can find them.

Bitcoin Classic UAHF notices it is not on the Cash chain and as such will start to find the common block by rolling back the history of the chain. After it finishes doing that, it is just a node that is behind and it will synchronize with the network to catch up.

Note that this won't work with pruning nodes. A pruning node can't rollback so many blocks.