As a System Administrator for CA PPM, typically attribute defaults and configuration changes are accomplished within Studio.
The Financial Module within the application is not fully integrated into Studio and some of the configuration settings are accomplished within the Financial Module and not in Studio.
Detailed Financial Plans have the following attributes that are managed within the Financial Module for setting 'default' values:
Grouping Attributes
Period Type
Start Period
End Period
The application uses defaults and built-in logic for the detailed financial plan properties of these fields based on the configuration of the Entity, Plan Defaults page. The option to 'Lock Plan Structure' on this page will make the 'Grouping Attributes' Read Only. The Period Type and Period Date fields cannot be marked Read Only. The ability to set up this configuration within the Financial module affords the System Administrator with the option to have different defaults for different Entities.
The Studio Objects for 'Cost Plan' and 'Benefit Plan' show these attributes and if you go into the attribute properties page, you will see the 'default' and 'read only' options for attribute definition. In the current design, making changes to this Studio Attribute Properties page for these specific attributes do not provide you with the ability to set the attribute to 'read only' or using the 'default' value on the detailed financial plan. Attempting to set the 'read only' option in Studio for these attributes does not actually save or set it to 'read only' and no error message is provided. Setting a 'default' value in Studio for these attributes is not used when creating the financial plans.
Login as a Financial Administrator - Navigate to Administration, Finance: Setup, Entities - Open an Entity and navigate to 'Plan Defaults' tab

For more information on the 'Freeze Date', Reference TEC439472: How does the Freeze Date on the Financial Planning Defaults work?
Checking the box to 'Lock Plan Structure' will not allow the user to change the 'Grouping Attributes' when creating detailed plans.