Can we make account null and non editable for Expense Template A

Summary:

Can we make account null and non editable for Expense Template A and for other templates it should be editable and default account

Content (please ensure you mask any confidential information):

The requirement here is if we have Expense Template 'A' which is for projects so the charge account should be null and non editable.
For other expense types it should as seeded functionality.

I was able to make the field non editable for Expense Template A and editable for others , however I am not able to make it null for Expense Template A.

Any help is really appreciated here.