When you change the Pk field of a table, that is a Rename() event, and by default this popup appears. There's no way to avoid this I think...
It's to avoid that a user accidentally changes the No. When you click Yes, the No. is changed and also updated in tables that have a relationship to it.
You could use the OnRename() trigger, or an event on it, to add some extra business logic to it.
Or, use a page extension to make the field not editable, to avoid the rename from happening and so also no popup...
