Hi Blake,

If you don't want users to access this button, simply set its visibility to false — this will hide the button, preventing users from opening the Pre Posting Assistant. If you intend to restrict access for a specific group of users or sites, you can achieve this by using a custom context.

Or,

If you need to make the fields read-only in the Populate Assistant window, follow the steps below:

Inside the page designer click on All Pages  → Assistants → Pre Posting with Source Assistant → Steps → Step1 → Single Pre Accounting List → Crudactions →  Edit → Enabled false (un check). 

(IFS Applications - 24.2.6)

Thank you.

much appreciated ​@SureshBandara