What does the cryptic crossword clue "Changed in last year, with an unpleasant impact (7)" mean?

The wordplay uses anagram, charade. anagram of INLAST ("in last") + Y (abbreviation of "year,") [anagram: "Changed"] = NASTILY The answer is NASTILY.

Changed in last year, with an unpleasant impact (7)

Guardian Cryptic #29517 | 26 Across | 2024-10-18 flower