Depends. If you're changing the block, you'll need to go puspakom for inspection and register the engine block number with JPJ. Same goes for auto to manual conversion.
If you're turbo charging, no need to do anything la. If it's just stroking, reboring, injectors, etc.. these mods are low profile and no need to be registered.
It's coming near to Raya and Puasa, so if you change exhaust, make sure it's not overly loud or big big tip. Sure kena in blocks.