Cannot set child table field property in Frappe v14

Hello, I’m currently working on custom apps development using Frappe and ERPNext version 14

I want to change some fields property in the child table of my custom doctype. I’ve successfully done this in Frappe and ERPNext version 12, however in version 14 the same code won’t work and I discover that the same behavior occurs in ERPNext doctype which is Asset Movement.

I’ve got the same error in browser console as Asset Movement in my custom doctype. It is expected that if I change Asset Movement purpose it will change the read only and mandatory properties in the child table of Asset Movement, but now it is not happening

Is there a different way in version 14 to achieve this?

thank you in advance