I've done some testing on this and it appears that the fields in the insert section are linked to the ones in the update section. If you remove the id field in the update section, the one in the insert section is also removed.
Also, if you uncheck the Update page on the initial wizard screen, the edits on the insert section will be in effect.
So if you don't want to allow the user to update the id, then you should make the change on the update section.
If you want to have id not in the insert, but in the update, then you would want to generate the pages for everything except update and then run through the wizard again to generate the update page the second time around.