Can i add my own vocals and re-arrange a song or lyric?

Yes. You would need to purchase a 'Derivative-Use-License'. You may then re-record it or re-arrange it, or re-mix it, or re-score for different vocalists or instruments. If a lyric, you may edit it and combine with audio content to make a complete song. A great buyer benefit of derivative license is that it also grants you an equal share of gross income from any CD or Download sales accruing worldwide from use of the derivative version (on a 50%/50% buyer/seller basis)!