Late answer, I also face a similar issue. We have tried using the custom classifier, but it doesn't work for a column that is used as a partition key.

What works for us:

1. Disable auto-add index for partition key in Glue crawler (in Glue crawler definition)

2. Manually (or programatically) update the partition column in the table schema definition in Glue as date (or whatever type you want)

3. Save the schema

4. Add (back) the index

I made steps 2-4 to be a create-or-update process every time crawling finishes