Change course, heading north (4)
I believe the answer is:
edit
'change' is the definition.
(editing is a kind of changing)
'course heading north' is the wordplay.
'course' becomes 'tide' (tiding is a kind of coursing).
'heading north' is a reversal indicator.
'tide' reversed gives 'EDIT'.
(Other definitions for edit that I've seen before include "Blue-pencil" , "Make changes to (text)" , "Redact, perhaps" , "Censor" , "work on newspaper?" .)