Here is a picture of the rear of a Premium bumper.
The fog lamps are attached to quite a large plastic moulding that is also used to hold the left and right part of the grill and the whole moulding bonded/glued to the bumper.
The middle parts of the grey plastic grill are attached using the studs that come through the bumper from the chrome grill surround.
The indicator lamps just clip in.
The foam inserts that fit between the bumper and the crash beam are different to the ones fitted to the facelift bumper.
So, the problems would involve,
Attaching the foglamps.
Sourcing the foam inserts.
The shape of the air ducting between grill and radiator is different for the Premium and Facelift bumper, so would need modifying.
Fixing inserts beneath each indicator.
Fitting/making a filler piece for the wheel-arch [the Premium bumper is wider at the lower wheel-arch than the Facelift]
None of the above would be insurmountable, just need to be aware what is needed.
Dave T