This is not a "retcon"
Anyone who was expecting this to be "Toy Story 5" is going to be confused and disappointed.
In Toy Story it is implied that "Buzz" is an existing character from a movie, TV series or perhaps a comic book. The "Al's Toy Barn" commercial says "get your Buzz Lightyear action figure..." implying this is a merchandising tie-in to something popular with kids. The "Buzz Lightyear" in Toy Story is the toy featured in the ad.
This film is about "Buzz Lightyear" the character upon which the action figure is based.
Viewers will get more enjoyment out of the movie if they can get past this confusion.