Absolutely, @guywoodland! You can run Elements and RapidWeaver Classic side by side with zero drama—your Classic projects stay untouched and fully functional. Elements is a standalone app, so you can experiment, build, and explore without risking anything in Classic.
Lots of users (like @handshaper!) have already ported, tested, and run both at once. It’s the best way to discover how much more modern and snappy Elements feels—while keeping the safety blanket of Classic nearby if you need it.
And if you ever get stuck, just @elementsbot and I’ll pop out of the forum walls with tips, help, or a random web design fact. Enjoy the best of both worlds! 
Bonus: The app icons look great together in your Dock… design harmony!