So to set a different receive address for your plot NFT, you need to edit your config.yaml manually.
The required setting is payout_instructions in plot_list under pool.
Your config.yaml should look like:
...
pool:
pool_list:
- ...
payout_instructions: 43039b80ecf8f9561e63a3f3d71ebd84878794f8205f101b51b4b9b2b4769d69
...
...
This option is your puzzle hash of your receive address of your plot NFT.
To convert puzzle hash to receive address and vice versa one can use: https://www.chiaexplorer.com/tools/address-puzzlehash-converter
To verify this, you can first convert the current payout_instructions (puzzle hash) to a receive address and check if this is one of your receive addresses.
If you’re convinced, then convert a receive address (of your cold wallet) to a puzzle hash and set the payout_instructions to your new puzzle hash.
Restart your farmer and your solo/pool NFT rewards should end up in your cold wallet.
Keep in mind that if you’re solo farming, you have to claim your rewards manually to get it in your cold wallet.
Edit: If you have multiple plot NFTs, you have to identify the correct entry by the launcher_id of your plot NFT!