Since its a bit difficult to to find developer related information for Bitcoin Cash I'm asking here. What changes would be required from a mining-pool developer's point of view to also support Bitcoin-Cash?
This could potentially work out of the box I believe.
You don't need to worry about replay prevention, or any of that when dealing with outputs generated by mining a block. These are new outputs and they aren't (under normal circumstances) available in the Bitcoin blockchain. The BCC client might even provide this protection by default, I don't know. But once you do a payout to a miner, they will certainly add replay prevention if they spend their BCC by default.
I suggest you modify the existing BTC tag (instead of adding a new coin BCC), https://github.com/coinfoundry/mining-core/blob/master/src/MiningCore/config.json#L218
Change those lines to work with the Bitcoin Cash daemon, instead of connecting to the Bitcoin Core client. Also make sure to modify the pool address to yours.
But I want to run both bitcoin and bitcoin cash - how do I do that? I'm not going to do the work for you, there are multiple changes required and nobody here will be able to answer you to the full extent. I suggest you edit the BTC tag just because it great simplifies the amount of explanation I have to do and allows you to test if that works before even thinking about an engineered approach. People here generally don't answer software engineering questions, let alone those that involve BCC.