How to update/edit existing schema in customer attributes

In the current People core services setup for a client, we already have an existing customer attributes schema which is uploading 65 customer attributes along with the data within that. Subscriptions are also added for Target and Analytics, where we are sending all of these 65 customer attributes to Target as well.

As part of a use case, we need to add 5 new customer attributes to the schema. Here are few questions we have:

1. Is it possible to edit the existing schema to add 5 new customer attributes, so that the existing schema has a total of 70 customer attributes?  As per the documentation in experienceleague, it is possible to edit the existing schema, but I do not see any option to do it in the UI
2. What is the best approach to address this scenario?
3. Is there any way to download an existing customer attribute schema (which has 65 attributes)?
4. Is there any way to export/download the list of customer attributes being used in Adobe Target ? We can see the list under the “Configure Subscription” section, but how do we export the list?