Elastic/NEST 2.0+ how to avoid some characters in the auto-generated Id "_id"?

Elastic Stack Elasticsearch
1

When indexing a new document with an auto-generated id there is some characters in the Id (_id) I would like to avoid.
Sample Id : AVaeUlLX_DM3y2eId2rf
Typically I don't want _ or - characters.
Is it possible to setup this somewhere (with a pattern +/- style) ?
Or, is this feature can be possible and added in future ?

( At the moment I've a nasty trick to avoid the problem by checking the Id of the document. I delete it if it contains characters I don't want then re-indexing, ugly loop yes but now this is how it works for me. )

Any help or idea appreciated.