The short answer: if your project changes the structure of the building, or adds floor area, you need a BCA General Builder. If it's interior refinishing โ carpentry, paint, new flooring, new bathrooms without moving plumbing walls โ you need an HDB-licensed renovation contractor.
We're a BCA General Builder Class 2. My sister's company, Larry Contractors, is HDB-licensed for renovation. Different licences, different scope, different specialisations.
When a client calls us and the project is really renovation in disguise, we refer them to Larry. When a client calls Larry and the project is really structural, they refer us. Keeps the work with whoever's actually licensed for it.