Perks up when crossing Northern Ireland with friend (8)
I believe the answer is:
animates
'perks up' is the definition.
(animating is a kind of perking up)
'when crossing northern ireland with friend' is the wordplay.
'when' becomes 'as'.
'crossing' is an insertion indicator.
'northern ireland' becomes 'ni'.
'with' says to put letters next to each other.
'friend' becomes 'mate' (mate is a kind of friend**).
'ni'+'mate'='nimate'
'as' placed around 'nimate' is 'ANIMATES'.
(Other definitions for animates that I've seen before include "Enlivens" , "Gives life or movement to, say cartoon" , "Brings to life" .)