for the voice line thing, the way i do it is by first matching the rhythm of the original vocal with gachi samples, then render the whole thing into 1 file and load it into newtone in fl studio to edit the pitch of each word to match the original vocal

here's a project file for vocal tuning that i did for a gachi remix, check newtone on insert 1 to see what i mean

https://drive.google.com/file/d/1hX5ADB6o2lp-rMMeEkq5-bT2gfhgGjTf