Need to Restrict or hide the + icon in AR transaction page

The customer wants to customize a page to validate a user-provided transaction and, after validation completes with status 'N', prevent the user from adding new lines or making further changes. They have tried using the page composer but found it not feasible and are seeking alternative ways to freeze the form after validation through page customization.

For the above Issue , we got the response from SR that it is not feasible to freeze the complete page in oracle composer , or even to hide the + button in the page. By using Sandbox. Please provide any idea here. We want to restrict customer to change any thing after the page is validated by a custom validate button.