Does the cost on a Change Order Sub count before the change is approved?

Yes. The amount you enter in the Cost field on a Change Order Sub counts in the final forecast straight away, regardless of status. You do not need to wait until the change is approved. The cost claim from the subcontractor does not affect the final forecast until the change is approved.

When the change is set to Approved, Cost is set equal to the cost claim. When it is set to Rejected, Cost is set to 0. If you do not want the change to affect the final forecast until it is clarified, leave Cost at 0. If you have not received a specific claim yet, you can set aside an estimate with an Expected Addition instead.

Read more about the difference between Uncertainty and Expected Addition in Uncertainty and Expected Addition, and about the statuses in What do the statuses on a Change Order Sub mean?

See also What is the difference between cost, cost price, cost claim, income requirement and income?