It will work without problems to open old projects from the pirated version. (In fact, old projects from the official Japenese versions will create problems!) It will offer you to upgrade your engine and it will show you what changes there are. It will also warn you about the different RTP. There are basically two major things you have to consider:
- If you use any patches, they will be removed, because the engine is upgraded.
- Since the official version uses a different RTP than the pirated version, references to RTP files might broken because the filenames differ. So, make sure you import/copy all the files from the old RTP which you use into your project, or change the references in your game to the corresponding files of the new RTP.