How do I lock ratings on assessment form for managers however allow comments and updates

Summary:

We open up the assessment form for managers to enter their assessment, comments and ratings for year end performance management. However on a particular date they cannot update their ratings anymore but they should still have the ability to update the comments and assessments. Therefore the whole form is editable except for the rating. Ideally we want them to see the rating on the form but just can't update it.

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

24C

Code Snippet (add any code snippets that support your topic, if applicable):