Can I delete or rename a schema in Panther?
It is not possible to delete or rename a custom schema, but it is possible to archive a custom schema. This is not the same as deleting it because there are a few caveats (the schema cannot be currently used by any log source, and you will not be able to create schemas in the future with the same name), but you can archive one and create a similar one under a different name.
Custom schema field editing is possible. Please see Panther's documentation for instructions on editing: Editing a custom schema.