Changes begin, virtually, with a zodiac sign (6)
I believe the answer is:
varies
'changes' is the definition.
(I know this)
'begin virtually with a zodiac sign' is the wordplay.
'begin' indicates taking the first letters.
'with' is a charade indicator (letters next to each other).
'a zodiac sign' becomes 'aries' (I've seen this in another clue).
The first letter of 'virtually' is 'v'.
'v'+'aries'='VARIES'
(Other definitions for varies that I've seen before include "Tends to change" , "'Alters, changes (6)'" , "Changes, deviates" , "Differs, changes" , "Makes or becomes different, changes" .)