I'm wondering if this is possible/legal/correct or not...

Situation:
Developer has submitted a ground plan to authorities on building a project (let's say, apartment project). Halfway through, the developer want to add in more carparks for residents by reducing some of the pavement/trees/grass. Can the developer build these new carpark lots immediately on these spaces without re-submitting the plan to the authorities, or have to wait until OC is obtained and then "remove" the pavement/trees/grass to build the carpark lots?

This came across my mind and I asked my friends and I got pretty vague answers.