Some years ago the RAAF had quite a few Hornets sitting around awaiting engines [overhauls and repairs]. This was caused by our material mob not pre-ordering enough spares. One cannot snap fingers and acquire parts and components. the OEM's don't hold warehouses full of bits due to cost etc. Xmas treeing aircraft has been around since the Wright Bros. The airlines swap parts or take bits off others on the line or in maintenance all the time.