Changing into neat Roman embroidery (13)
I believe the answer is:
ornamentation
'embroidery' is the definition.
(thesaurus)
'changing into neat roman' is the wordplay.
'changing' is an anagram indicator.
'into'+'neat'+'roman'='intoneatroman'
'intoneatroman' with letters rearranged gives 'ORNAMENTATION'.
(Other definitions for ornamentation that I've seen before include "Adornment" , "Decorative work" , "Decoration, embellishment" , "Detailed artistic embellishment" .)