Modified ginger beer comes first -- about time (7)
I believe the answer is:
Here is my best explanation:
'modified' is the definition.
('altered' can be similar in meaning to 'modified')
'ginger beer comes first about time' is the subsidiary indication.
'ginger' becomes 'red' (red ginger is a kind of ginger).
'beer' becomes 'ale' (I've seen this before).
'comes first' is a charade indicator (letters next to each other).
'about' is an insertion indicator.
'time' becomes 't'.
'red' put after 'ale' is 'alered'.
'alered' placed around 't' is 'altered'.
(Other definitions for altered that I've seen before include "Changed, adapted", "Changed, modified", "Change", "Metamorphosed", "Treadle (anag)", "Converted", "Different", "Reformed" and "Modified".)