I'm not able to follow what you're trying to do.
Mapping has meaning to Elasticsearch, so this is harder to parse.
This is confusing as well. A reindex operation doesn't necessarily need anything new to work. If I had to guess at what you're describing, it's that you want to use the elasticsearch input plugin to read your existing index, and then use the values from this csv to somehow convert fields in the old data into two new fields for the target indices? Is this correct?
If so, you should read up on the translate filter plugin, which should allow you to use the csv to accomplish this.