Adding analyzers during runtime

My story is simple.
I have an index of 65 millions records working on production system.
In a new version, I'd like to make some changes in query logic, that needs some mapping updates.
To be more precise, I'd like to to change standard analyzer of particular field to analyzer based on path_hierarchy tokenizer.
I understand that the change needs reindexing of the field, or even field duplication, and I'm ok with that. This is not a problem. The real problem is that I can't figure out how to configure new analyzer on existing index, and update mapping by adding new field analyzed by a new analyzer.
Is it possible? There is no such option in index _settings API.
From my point of view, updating mapping by adding new fields, including merging mechanism is a killer feature. By adding the possibility to use new analyzers for new fields, existing "dynamic schema" nature gets additional feature - "dynamic capabilities".
Am I missing something in theory?
I didn't find anything searching over the mail list related.

Thanks