I'm trying to think of some examples. At present, I can think of two: the phrase "buck naked" was misheard and misrepeated as "butt naked", which has become a new standard. Although it is technically incorrect, it has become so universal that it is becoming a new standard. Similarly, the phrase "hate on" is currently a popular grammatically incorrect usage. If it survives long enough, it might end up becoming normative.
Interestingly enough, incorrect usages can become normative and still continue to be incorrect. The best example of that is "ain't", which persists in the language and persists as an example of incorrect usage at the same time.
On spelling, changes are rarer. One notable example would be the accepted use of "lite" instead of "light".
ἡ δὲ κἀκ τριῶν τρυπημάτων ἐργαζομένη ἐνεκάλει τῇ φύσει, δυσφορουμένη, ὅτι δὴ μὴ καὶ τοὺς τιτθοὺς αὐτῇ εὐρύτερον ἢ νῦν εἰσι τρυπώη, ὅπως καὶ ἄλλην ἐνταῦθα μίξιν ἐπιτεχνᾶσθαι δυνατὴ εἴη. – Procopius
Ummaka qinnassa nīk!
*MySmiley*