Sure, they don’t have to as they have you as a captive buyer.
Doesn’t mean you can’t ask. Worse they can say is no.
I’ve successfully done it on a number of items. On flooring and big ticket items, when upgrading over the base tier. It’s a win win as they make more margins on the upgrades over just slapping in the base stuff that the builder negotiated for.
Don’t ask the builder. Ask the up-grader in the show room at the time of pricing out and signing off on the upgrade.