Question changed to be more specific
Firstly I'm using SilverStripe 2.4.7. I am tearing my hair out trying to figure out how to do this and I need to help.
Ok so I have a dataobject and I use a dataobjectmanager on the admin's page to look after all of the dataobjects. I also use dataobjectmanager on other user's pages to look after the dataobjects that only relate to them. So the fields in the dataobject are used in the popups on both types of pages (the admin and the user pages).
I need to add a checkbox to the admin page popup only so that when they create one of these dataobjects they can select multiple users and then the ids are saved in a linked table. I hope I'm being clear.
I have my getCMSFields function in my dataobject (Offer) and getCMSFields in AllOffers with a dataobjectmanager. how to I add the checkbox without adding it to every other page too?