The preciousblock RPC treats a block as if it were received before others with the same work.
preciousblock "blockhash"
*bitcoin-cli help preciousblock
preciousblock "blockhash" Treats a block as if it were received before others with the same work. A later preciousblock call can override the effect of an earlier one. The effects of preciousblock are not retained across restarts. Arguments: 1. "blockhash" (string, required) the hash of the block to mark as precious Result: null (json null) Examples: > bitcoin-cli preciousblock "blockhash" > curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "preciousblock", "params": ["blockhash"] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/