Are you on board to use these built-in songs? Have you licensed them with Piapro or whoever the rights-holders are?

If not, I can provide stepcharts for music released for free use.

Nope, the songs are not licensed. The authors copyright policy and StepMania’s policy allows me to use that charts in a non commercial open source project unless copyright policies change

The short answer is: No

So yeah! Thank you for your help! I’m not good with charting