Cosmetic change finally applied to the old boat (8)
I believe the answer is:
eyeliner
'cosmetic' is the definition.
(I know that eyeliner is a type of make-up)
'change finally applied to the old boat' is the wordplay.
'finally' says to take the final letters.
'applied to' means one lot of letters go next to another.
'the old' becomes 'ye' (resembles a historical spelling of 'the').
'boat' becomes 'liner' (I've seen this before).
The last letter of 'change' is 'e'.
'e'+'ye'+'liner'='EYELINER'
(Other definitions for eyeliner that I've seen before include "instrument for enhancing lamps" , "Facial cosmetic" , "Make-up item" , "Type of make-up" , "Dark marks left by this" .)