If I understand right, you have applied the track motion composite level envelope to an event and you want to move this envelope without moving the event? Normally this envelop moves together with the event, but there is a little trick you can do to move the envelop without the event:
Select the track with the envelop and choose INSERT- EMPTY EVENT.
Place the empty event over the event with the envelop and make the length the same as the event with the envelop. When you now move the empty event forward or backwards, the envelop will follow the empty event. Next you place the new event that should contain the envelop on top of the empty event (at the same track).
Ofcourse, you can obtain the same result when you would like to move the envelop just within one event.
Theo