Is there any way to add a new case property to already submitted forms
You can use follow-up forms for already created cases to update existing case property and add new case properties. I recommend reviewing the case management documentation: Case Management - CommCare Public - CommCare Public
Case properties are distinct from the data captured in a specific form. Forms are able to set/update case properties that belong to a case.
Yes of course you can. But if you have already started capturing data, the new properties will only have data after you add them, hence it will empty before that.
Thanks to all for pointing me in the right direction.