How To Manage Projects With Significant Change Orders? 3 Days Onsite And The Change Order List Is ~10 Items Long

First and foremost, a strong project manager with knowledge and command in this field will help every variable you mentioned.

In your second paragraph you start in past tense with analyzing a job performed months ago. I think this exhibits your strong knowledge and command of how, what, why and if dissipated a few margins here and there.

You seek a deeper scope on how to reveal and combat these intricacies for financial game. This is perfect because as the provider and installer this is right up our alley.

1. Answer, if you see something, say something. Scope stipulations can encapsulate the unknowns and forewarn the stakeholder items expected as timely deliverables have not been qualified and can easily incur scope slip and cost overrun burden to 1 or multiple trades.

2. Contingency, if you have obvious scope differences discovered or revealed by your teams intelligence that forecast or impact should be rectified by the hand that is feeding you. Jumping in without scope transparency will lead to finger pointing deliverables and competency.

Let's say you propose your project at 150K, your engineer spent his heart out trying to tie it all together. The GC comes back and says....your price is low add 15% and resubmit.

This is not always the case, play your cards how you want. Protect yourself and those around you. No one bids a job at $10 bucks, break even is at $8.50 bucks and expects longevity with the remainder.

Analysis, Experience and Contingency is my go to, I would like to hear yours. Excluding(dinosaur Pelco fan boy era). 

This is where working directly for the owner on a project like this quickly turns into a nightmare. In the end this will often end up costing the owner more than if you worked directly for the GC. The GC should be tracking all of the change orders but will they share that information with you on a regular basis and keep you informed on what is going on before everything gets covered up. Be prepared to fight and argue on what you are supposed to get paid for.

Depending on how fast the construction is going and they won't do T&M you might be able to do the change orders as they come up instead of all at once.

For the customers sake it will most likely be less expensive if they will do T&M. It is hard to estimate projects like this that change constantly. What you may think will take 12 hours ends up only taking four or vice versa. The hard part for you and your staff is keeping track of what is a change order and what is part of the original project. Oftentimes you will leave money on the table if you do T&M for the change orders as it is hard for the techs to separate out the hours between the two. Well it's not hard but when they are out there busting their humps keeping up they forget to track what was what.

Good Luck 

Make sure the right person signs for the request before delivering.  Not just anyone, the right one.  Which means identifying in writing, in advance, who can authorize changes and to what dollar amount.  If you want to get paid. 

1st know your products, not just sales, ins, outs  

2nd know what you can and cannot accomplish , help needed from others

3rd know what the true cost are , materials, labor, burden etc

4th know what the competition is getting and how they operate so you can recoup funds  

5th be real with yourself and your employee base , what, how, Time constant

most important is know what your doing, talking about, and conveying this to the management , some Don't have a clue and after the dust settles you will leave as the best or worst

have a great structure of accountability in place to oversee the change s and make sure there in place properly

last and most important

GET the Right signatures, authorizations, paperwork to get Paid and not end up in a haggle over who s who and what was and what was not said

Always in Writing , never word of mouth

old saying Good intentions pave the way to disaster