Let ua forget about GMConnects because it is always at least 24 hours behind and reframe your question.
Changes can always be made, but you are asking when is it too late to make a change and not have to start all over at the very beginning and we will make that your question.
2500 and you can make a change w/o prejudice. 3000 and it is possible that a change can be made, but at your dealers request and even then not always.
A color change should be possible unless the color is on constraint.
After 3000 it is not feasible - the car will be built as ordered and the dealer who ordered it will be responsible for paying for it. Remember, every vehicle Chevy produces is already sold because dealers are the customer. Every Chevy you see sitting in the showroom or on the lot has been bought by the dealer. If the car is never sold, the dealer eats the cost.
I monitor this site, so if you need clarification post and I will try to clarify.
Laborsmith