The hardest part of replacing the control arms &/or ball joints on a coil spring suspension is getting the bolt holes to line backup while fighting the suspension tension. You’ll want really big pry bars or ideally someone to help you hold & leverage the suspension into the proper place. Obviously compressing the cool spring will also help but I personally do them without doing that. As for the OP’s question, bleeding the air bags down is stupid easy. Remove the rear cargo cover & sub covers & loosen the 2 air line fittings. Make sure you pull the air pump fuse first, or disconnect the battery.

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Current vehicles
2001 325XI
2006 X5 3.0
2004 X5 3.0