Much thanks! I find that STEEM has many interesting features that relay on custom_json. Look how to reblog/resteem a post with sign_transaction and cli_wallet:

sign_transaction {"id": "follow", "json": "[\"reblog\",{\"account\":\"dropahead\",\"author\":\"yoganarchista\",\"permlink\":\"just-a-little-gif-i-created-with-a-collage-artwork-of-mine-100-power-up\"}]", "required_posting_auths": ["dropahead"]}

And this is how to reblog with a JSON-RPC call to cli_wallet:

curl http://127.0.0.1:8093 --data '{"jsonrpc": "2.0" "method": "sign_transaction", "params": [{"operations": [ ["custom_json", {"id": "follow", "json": "[\"reblog\",{\"account\":\"dropahead\",\"author\":\"yoganarchista\",\"permlink\":\"just-a-little-gif-i-created-with-a-collage-artwork-of-mine-100-power-up\"}]", "required_posting_auths": ["dropahead"]}] ] }, true], "id": 1}'