Alright, to copy over Shifts, Warps, and Signs and fix them for the new room locations, do the following:
Make sure you've copied all the rooms first, then open World.ini.
Any room that has a Shift, Warp, or Sign will have have its coordinates appear in World.ini in brackets as a section header. So copy one such line and all lines that follow it.
EXAMPLE
[x1004y1009]
Sign(a)=You're chicken.
Sign(B)=No, you're the chicken.
ShiftYMap(A)=2
ShiftType(A)=3
ShiftQuantize(A)=False
ShiftVisible(A)=False
ShiftEffect(A)=False
ShiftSound(A)=Switch
ShiftType(C)=2
ShiftXPos(C)=5
ShiftXMap(C)=1006
ShiftYMap(C)=996
ShiftTouch(C)=True
ShiftAbsoluteTarget(C)=True
You would copy and paste the code into the big level's world.ini. Then you would find the original x1004y1009 the editor, take a good look at it, and then look for where you put that very same screen in the new level. In World.ini for the new level, you would then change the coordinates in the brackets accordingly so that they point to the correct screen.
Note that if a Shift has the ShiftAbsoluteTarget=True flag, then you have to do the same procedure listed above to find the correct numbers for ShiftXMap and ShiftYMap. So for this example I would also have to find out the new coordinates of x1006y996, because Shift C does have AbsoluteTarget enabled..
FINISHED EXAMPLE IN NEW LEVEL
[x994y980]
Sign(a)=You're chicken.
Sign(B)=No, you're the chicken.
ShiftYMap(A)=2
ShiftType(A)=3
ShiftQuantize(A)=False
ShiftVisible(A)=False
ShiftEffect(A)=False
ShiftSound(A)=Switch
ShiftType(C)=2
ShiftXPos(C)=5
ShiftXMap(C)=996
ShiftYMap(C)=967
ShiftTouch(C)=True
ShiftAbsoluteTarget(C)=True(!!!)