Ctrl+p/Ctrl+n to arrow up/down (slack) using karabiner

karabiner.json

                "rules": [
                    {
                        "description": "Ctrl+p/Ctrl+n to arrow up/down (slack)",
                        "manipulators": [
                            {
                                "conditions": [
                                    {
                                        "bundle_identifiers": ["com.tinyspeck.slackmacgap"],
                                        "type": "frontmost_application_if"
                                    }
                                ],
                                "from": {
                                    "key_code": "p",
                                    "modifiers": {
                                        "mandatory": [
                                            "control"
                                        ]
                                    }
                                },
                                "to": [
                                    {
                                        "key_code": "up_arrow"
                                    }
                                ],
                                "type": "basic"
                            },
                            {
                                "from": {
                                    "key_code": "n",
                                    "modifiers": {
                                        "mandatory": [
                                            "control"
                                        ]
                                    }
                                },
                                "to": [
                                    {
                                        "key_code": "down_arrow"
                                    }
                                ],
                                "type": "basic"
                            }
                        ]
                    }
                ]