Lot's of open source software licences and I got confused in the maze once. I'd doubt there is one that would prevent your own modifications for your own personal use but if you were to make your modified version available to others, I think you should always be both making clear that what is on offer is a patched in some way version and making your code available. (Again, not that I'd even understand say Audacity code, let alone modifying it)

Back to the recorders, we have another Zoom here, the H4. Am aware of the H6 too. Nice in that it's got knobs on to adjust levels and a larger screen helps getting older eyesight but I think beyond the possibly "carry in your pocket" size which, to me, the H2 and H4 achieve.