Warns of later modification (second) (6)
I believe the answer is:
alerts
'warns' is the definition.
(alerting is a kind of warning)
'later modification second' is the wordplay.
'modification' indicates anagramming the letters.
'second' becomes 's' (common abbreviation).
'later' is an anagram of 'alert'.
'alert'+'s'='ALERTS'
'of' is the link.
(Other definitions for alerts that I've seen before include "Warns, draws attention to" , "Alarms, warning signals" , "Puts on guard, warns about impending danger" , "Puts on guard, forewarns" , "danger-signals" .)