Once you edit the frame in form1 you will not be able to automatically get the changes in original frame1.pas /dfm.
until you edit any items in the frame in the form1 ,there is only a few information is in the form1.dfm so all the properties in the frame.dfm are used , but after editing in form1 the form1.dfm will have some information about the changes you did, so they will override the original frame1 properties So now you cant expect an automatic update.
If there is no any need to modify the frame in the form1(You said you need to modify the original one and if you modify both(original and the one in form1) it will definitely confuse you.
So do the changes in original one only, After finalizing that you can do changes in the forms you are using the frame.(because you may need to use specialized frame in different situations)
Or you can call the frame in run-time if all the instances of your frames are going to be the same
var
myframe :TFrame ;
begin
myframe := TFrame2.Create(self) ;
//better using a panel as a place holder
myframe.Parent := Panel1 ;
myframe.Show ;
myframe.Left := 0 ;
myframe.Top := 0 ;
end;