Feel intense sorrow for first mate after change of rig (6)
I believe the answer is:
grieve
'feel intense sorrow' is the definition.
(I've seen this before)
'first mate after change of rig' is the wordplay.
'first mate' becomes 'eve' (I've seen this before).
'after' says to put letters next to each other.
'change of' indicates an anagram.
'rig' anagrammed gives 'gri'.
'eve' after 'gri' is 'GRIEVE'.
'for' acts as a link.
(Other definitions for grieve that I've seen before include "Feel deep sorrow as for a death" , "Mourn, feel sorrow" , "Suffer great sorrow" , "Cause great distress to" , "Feel intense sorrow at someone's death" .)