OP, and any new-to-Tesla Energy potential customer, yes the phone number
@jaed supplied above is the number to call right now since everyone from Energy started WFH. We were assigned an advisor when we ordered (this has changed a few times over the past few months) but Energy has told us that really anyone who answers can help you and we've found that to be true. The person answering can pull up your order and see what is going on such as permitting etc. and if they need to direct your request to another department such as design for panel layout they get in contact with them so you don't have to deal with many different people and explain everything over again.
We changed our solar layout before signing. We didn't want any panels on the front of our house and the design team was able to rework the layout among all of our roof vents to fit the three panels in question to the side and back sections. Not quite as nice of a panel layout at initial design but it worked for us to get everything onto two roof sections. Just so you are aware, there are distance limitations as the panels get near the hips or ridge. We also during this covid down time decided to add another PW to our order. So yes, totally doable to make changes. They re-did our contract and since our permit was already approved by the city for our initial two, they had to file another permit for the extra one. We were told cities they had worked with before let them simply amend the original permit in cases like this but our city didn't; but they handled all of that from their end and we got that permit approved, now waiting on scheduling.
In our area Tesla is working with PG&E, our electricity distributor, and there are some incentives through them in addition to the Federal ones. Our city doesn't have any financial incentives so if yours does that's great. In our case Tesla applied for an application for a PG&E incentive for us, but until the work gets finalized I don't think we have any guarantees if that will come through due to PG&E funding for the program and how many people are ahead of us on a waitlist. The Federal IRS incentive will require you to qualify for it (your tax preparer can help you determine that). Really not unlike EV incentives with Municipal, State and Federal programs.