In Sana admin, it should be possible to import and export product specifications and product attributes. Managing the specifications and attributes from Sana admin is troublesome and tedious when you have several hundred attributes.
For product specifications, you should be able to export a csv or xlsx list of both the already defined fields and the available fields. You could then easily define in Excel (or similar) which fields you want included in the specifications, visibility true/false for the different pages and sort order, and import to Sana.
Similarly for Sana Product Attributes, you should be able to manage existing and create new attributes with import/export functionality.
Additionally PIM users should be able to manage this from the PIM and sync to Sana as a scheduled task, ensuring that the product data in Sana is always up to date.