Ok. Please be aware that it will be slow in comparison of doing that at index time (using ingest or not).
May I ask what is your goal at the end?
Also could you provide a full recreation script as described in About the Elasticsearch category. It will help to better understand what you are doing. Please, try to keep the example as simple as possible.
A full reproduction script will help readers to understand, reproduce and if needed fix your problem. It will also most likely help to get a faster answer.