Yes, there are general limits as to what they can do. The type of change you describe is drastic and would require a re-review of the plans (changing from SFR to condos). There is already a specific density requirement for the project and as long as they stay within those density requirements, they can make changes, but SFRs to condos is a major change.
For builders like 4S Ranch and Del Sur, they are already almost finished. They do not have any new plans at the tentative map stage (which is where they could negotiate changing SFRs to condos). The only possible change they could do (which is what some builders have done) is build smaller and more affordable houses in order to meet demand at that price range. Still, changing in midstream like this requires a lot out of a builder, their construction crews, and design.
