Done with the command line client "cli_wallet".

sign_transaction { "operations": [ [ "comment", { "parent_author": "steemitblog", "parent_permlink": "important-notification", "author": "abit", "permlink": "re-steemitblog-important-notification", "title": "Re: Important Notification", "body": "THE BODY", "json_metadata": "{\"tags\":[\"steem\"],\"app\":\"steemit\/0.1\",\"format\":\"markdown\"}" } ], [ "comment_options", { "author": "abit", "permlink": "re-steemitblog-important-notification", "max_accepted_payout": "0.000 SBD", "percent_steem_dollars": 10000, "allow_votes": true, "allow_curation_rewards": true, "extensions": [] } ] ], "extensions": [], "signatures": [ ] } true