Create a new index when document has a particular field?

Is it possible to create a new index everytime my document has a particular field updated? say all docs with 'tenant':"100" are part of one index and if a document comes with a field "tenant":101, a new index is created? can this be accomplished with index templates?

You should be able to change the index name based on such a field in the data through an ingest pipeline. Whether that is a good idea or not is a different question though. It probably works for smaller number of tenants, but is unlikely to scale well.