Artist with Welsh name who transformed old entertainment (5-4)
I believe the answer is:
raree-show
'old entertainment' is the definition.
(historical type of street show)
'artist with welsh name who transformed' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'with' means one lot of letters goes inside another.
'welsh name' becomes 'rees' (common Welsh name).
'transformed' is an anagram indicator.
'who' with letters rearranged gives 'how'.
'rees' inserted inside 'how' is 'reeshow'.
'ra'+'reeshow'='RAREE-SHOW'
(Another definition for raree-show that I've seen is " entertainment".)