The trigger to that change would be a job cost system in the field PM office that would track the 'proposed' and potential change order costs in sufficient detail to account for the earned revenue but to also not fool yourself by confusing "earned" and billable with Collectible.
I had a buddy who owned a drywall subcontracting firm who, when asked how a particular project was going, would say, "I'll know when I collect the retention."
LOL, understood, but your buddy is a subcontractor and at the mercy of the integrity of the prime contractor. Halliburton would be the Prime and would be dealing directly with the owner or the owners professional representative.