If I create something using the free version of Suno and then subscribe to a paid plan, can I use the content created with the free version for commercial purposes?

Even if you subscribe to a paid plan later, content created with the free version is strictly limited to non-commercial use. This remains the case even if you use the Remaster feature to regenerate the content.

If you really want to use it commercially, you should try contacting Suno via email to see if you can obtain permission.