Require alteration to top line in decorative work (11)
I believe the answer is:
needlepoint
'decorative work' is the definition.
(decorative embroidery)
'require alteration to top line' is the wordplay.
'require' becomes 'need' (synonyms).
'alteration to' is an anagram indicator (the order of letters is altered).
'top'+'line'='topline'
'topline' with letters rearranged gives 'lepoint'.
'need'+'lepoint'='NEEDLEPOINT'
'in' is the link.
(Other definitions for needlepoint that I've seen before include "Work on canvas" , "lace" , "craft" , "Closely-stitched embroidery" , "depicting feature of Isle of Wight rock?" .)