Can I just copy/paste at the end of the songs.dta or is there some metadata that I would corrupt?
Yes, songs.dta is just a text file so you can copy-paste in it, just make sure you don’t miss any bracket or parsing will fail and the game won’t load any songs after the parsing error.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!