A couple changes that took place after '55 in which Elvis played a big role were the extent and permanence of the popularization of rock, and the shift in marketing for all kinds of products from adults to youth.
But that started before Elvis was big, things like Davy Crocket hats and hula hoops and rock and roll were marketed to kids before Elvis was known nationwide. Once Alan Freed came to NY in the fall of 1954 the white kids picked up on rock and roll rapidly. Check out this chart from NYC's top 40 station, before "Heartbreak Hotel" had become big.
WMGM Top 10 Survey
For the Week of March 5, 1956
1 1 ROCK AND ROLL WALTZ - Kay Starr (RCA Victor)
2 2 LISBON ANTIGUA - Nelson Riddle & His Orchestra (Capitol)
3 4 THE POOR PEOPLE OF PARIS - Les Baxter & His Orchestra (Capitol) 4 8 WHY DO FOOLS FALL IN LOVE - The Teenagers featuring Frankie
5 3 NO, NOT MUCH - The Four Lads (Columbia)
6 6 MORITAT (A Theme From “The Three Penny Opera”) - The Dick Hyman
Trio (M-G-M) 7 7 THE GREAT PRETENDER - The Platters (Mercury)
8 5 SEE YOU LATER, ALLIGATOR - Bill Haley & His Comets (Decca)
9 10 MEMORIES ARE MADE OF THIS - Dean Martin (Capitol)
10 9 BAND OF GOLD - Don Cherry (Columbia)
There's already three classic rock and roll songs in the top ten in NYC BEFORE anybody there knew who Elvis was.