Most of us have estimating programs nowadays. When I do a change order, I always do it in the estimating program. There are many ways to get around ridiculous requirements like 10% profit and overhead. Extra length on conduit, upping the price of material before it gets to the extension, etc. Make sure you charge for things like bond, equipment rental, warehouseman, and especially every minute you spend, talking about, laying out and pricing the change order. However, always keep something in your pocket, for example the Foreman's truck or a tool that had to be delivered. If you get grilled by the GC, tell him flat out that you will review the change but unless there is a blatant mistake every minute you spend will be charged to the change order, so even if you skim $10 off of it, it may cost them $20 in your time to do it. Given that you always hold something back the best answer you can give when they question is, "Thank you for making me go back, while I corrected the item you identified, I realized I hadn't charged for the tapconns so your price actually went up. Thank you again." If they try to argue about Project manager time, get a copy of the NECA manual of Labor Units or just reference it. It CLEARLY states that the labor units included do not cover supervision. I, as a project manager, am not assigned to only one project so, no change orders, no time sent. change orders, additional time spent. Period.
I will say that I RARELY have a problem with change orders. I share the estimating data right up front most of the time and if not, when they ask for it I give it to them 10 minutes later so they know I didn't have to make it up.