Once I add Products to the Opportunity I can no longer edit the Opportunity's Amount field. Is it possible to change that amount so that it is saved on the Opportunity as a different amount? Possibly with workflow or a trigger? I tried a workflow and it looked like it didn't work.
From the help:
For opportunities with products, the amount is the sum of the related products. You cannot directly edit the amount unless the opportunity has no products. To change the amount for an opportunity that contains products, edit the sales price or quantity of the related products.