Mark’s account also mentions that Jesus is questioned because He is “the carpenter”. Matthew’s account says that He’s “the carpenter’s son”.
Bingo! Now let's talk about what it means...
Most people ignorant of Jewish culture dismiss this as irrelevant, but nothing could be further from the truth. They write it off because they assume that Jesus simply assumed the family business, as it were.
But Matthew had to clean up the scandal that Mark heavily implied. In ancient Israel, as in most patriarchal societies, you are identified as the son of your
father. To identify you as the son of your
mother is to imply that paternity is either unknown or in dispute...
But there is no father of Jesus anywhere in Mark... Not so much as a passing mention, even though the crowd names the rest of his family...
(This comes up again in John 8:41, where a hostile crowd heckles Jesus with "
We were not born of fornication," implying that Jesus was.)
Now, Matthew lifted heavily from Mark in the writing of his own Gospel... 90% of Mark is contained in Matthew, and a good chunk of ghat is verbatim. Matthew started with Mark, and added onto the beginning (Mark has no birth narrative), and the end (Mark ends at the tomb, with no sightings of the risen Jesus)
With so much Mark in Matthew, anything omitted or altered becomes significant. Matthew is believed to be writing to a more Orthodox audience than Mark, and they're not going to abide even a hint of scandal about their Messiah...
So "the carpenter" becomes "the carpenter's son," Matthew gets to refer back to Joseph (who appears for the first time anywhere in Matthew's Gospel), and Mark's implied scandal gets defused.
You asked for evidence of an alteration; there you go.