This is a difficult question to answer. How much is too much? Where’s the line between tasteful and tasteless transformations? Is it ok to change a melody that’s known and beloved by multiple generations?
The answer ultimately boils down to a matter of personal aesthetics.
However, here are some general guidelines:
- The original statement of the melody should be mostly unaltered. Some minor adjustments are ok, but if you stray too far from the original the audience might not recognize the tune you’re arranging.
- Trust your ear first! Most people don’t think of music theory when listening to music. Many beginning composers make the mistake of focusing too much on the theory and, often, loose something in translation.
- Have fun! The more you enjoy what you’re doing the more it’ll come across in your work. Ultimately, this is your art and, if you like it and can stand by it, then that’s what matters most.