MariaDB 10.4

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create table my_table (id int auto_increment primary key, 
                       json_data json check (json_valid(json_data))
                       )
insert into my_table (json_data) values
('{
    "company": {
        "id": "",
        "name": "",
        "address": ""
    },
    "info_company": {
          "diff_v": "1",
          "grav_v": "",
          "diff_s": "2",
          "grav_s": "",
          "diff_g": "3",
          "grav_g": "",
          "diff_ri": "4",
          "grav_ri": "2"
    },
    "other_stuff": {
    	"diff_v": "1"
    }
}')
UPDATE my_table
JOIN (
  WITH jkeys_table AS (
    SELECT id, JSON_KEYS(json_data, '$.info_company') AS jkeys
    FROM my_table
  )
  SELECT id, 
         CONCAT('((?:',
                REPLACE(SUBSTRING(jkeys, 2, CHAR_LENGTH(jkeys)-2), ', ', '|'),
                ')\\s*:\\s*)"([12])"'
         ) AS regex12,
         CONCAT('((?:',
                REPLACE(SUBSTRING(jkeys, 2, CHAR_LENGTH(jkeys)-2), ', ', '|'),
                ')\\s*:\\s*)"([34])"'
         ) AS regex34
  FROM jkeys_table
) rt ON my_table.id = rt.id
SET json_data = JSON_REPLACE(json_data, '$.info_company',
                JSON_MERGE_PATCH(JSON_QUERY(json_data, '$.info_company'),
                                 REGEXP_REPLACE(REGEXP_REPLACE(JSON_QUERY(json_data, '$.info_company'), regex12, '\\1"<50%"'), regex34, '\\1">50%"')
                                )
                )

Rows matched: 1  Changed: 1  Warnings: 0


SELECT JSON_DETAILED(json_data) AS json_data
FROM my_table


json_data


{
    "company": 
    {
        "id": "",
        "name": "",
        "address": ""
    },
    "info_company": 
    {
        "diff_v": "<50%",
        "grav_v": "",
        "diff_s": "<50%",
        "grav_s": "",
        "diff_g": ">50%",
        "grav_g": "",
        "diff_ri": ">50%",
        "grav_ri": "<50%"
    },
    "other_stuff": 
    {
        "diff_v": "1"
    }
}