[YetAnotherMatt]

If you publish your transaction publicly then any miner can get the fees from that transaction. If you send your transaction only to your preferred miner, then only your preferred miner can get the fees from that transaction.

None of the standard software used for mining enables adding additional possible transactions manually AFAIK. It theoretically could be done though.

The only thing you need is to be capable of actually mining a block, which costs about 13k USD I've heard.

[dannyw]

Mining pools are run by teams of people whose full time jobs are to take care of their pool. I don't think any significant BTC or ETH pool runs standard software without any modifications.

I wanted to get a custom coinbase message included in a block, and paid $500 to a pool for the privilege.