Unable to access converted lead data via API

Greetings,
I’m working around with the Splynx isp admin APIs. I’ve noticed that converted lead data (including lead documents, lead quotes, lead info, …) are blocked from accessing (get/create/update/delete) we can only list them all out. But in the admin portal, we can perform all of these actions. Is there any way to update these entities in the API? Please help.

Thank you,