Keep making alterations to church by a pond preparing convert (4,3,6)
I believe the answer is:
chop and change
'keep making alterations' is the definition.
(I've seen this before)
'to church by a pond preparing convert' is the wordplay.
'to church' becomes 'ch' (common abbreviation).
'by' is a charade indicator (letters next to each other).
'preparing' indicates anagramming the letters (I've seen 'prepared' mean this).
'convert' becomes 'change' ('change' can be a synonym of 'convert'**).
'a'+'pond'='apond'
'apond' is an anagram of 'opand'.
'ch'+'opand'+'change'='CHOP AND CHANGE'
(Other definitions for chop and change that I've seen before include "Vacillate - keep altering plans" , "Keep on altering things" , "Repeatedly vary one's preference" , "Keep making alterations" , "Seesaw (metaphorically)" .)