There are signature riffs, and hooks that I rarely deviate from, especially when it's a sing-a-long favorite, like a "Brown Eyed Girl" - Imagine the DISconnect you'd get from the audience if you got "creative" with the Sha-lal-as in the bridge section? I try to channel the "vibe" of a song before I decide how to adapt it to my own personal style. I rarely copy the artist's style, unless it's for comic effect. I'm no mimic. That said - I think the lead vocalists that CAN do that effectively are usually very well accepted - just look at the popularity of the host of tribute bands. Seems like most of them try to really copy the originals, and with great success. My approach is a bit different, but valid, nonetheless. The audience makes the rules. If they like it ... they will come. If they don't .... you may as well play jazz.
(YIKES! Did I just say that?)