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Assuming you still have the connector on the end of the headunit then I would remove the trim panel in the car and you can disconnect your new unit without removing it by reaching underneath and behind the unit. Plug in the OE unit, eject the CD and reconnect the new unit. Replace facia panel and bob's your uncle.
Fastest way without doubt is to just plug the sucker back in. It takes 5 minutes to take the front of the dash off, then 5 to disconnect/reconnect/... then 5 to reassemble.