Pets reformed by present-day experts (6)
I believe the answer is:
adepts
'experts' is the definition.
(adept is a kind of expert)
'pets reformed by present-day' is the wordplay.
'reformed' indicates an anagram.
'by' says to put letters next to each other.
'present day' becomes 'AD' (as opposed to BC).
'pets' is an anagram of 'epts'.
'epts' after 'ad' is 'ADEPTS'.
(Other definitions for adepts that I've seen before include "Pasted by skilled people" , "Those completely skilled in their work" , "Proficient people" , "Very skilled persons" , "Pasted by experts" .)