Took care of primary change in date (10)
I believe the answer is:
maintained
'took care' is the definition.
Although both the answer and definition are past participle verbs, I can't see how one could define the other.
'primary change in date' is the wordplay.
'primary' becomes 'main' (synonyms).
'change' indicates an anagram.
'in'+'date'='indate'
'indate' is an anagram of 'tained'.
'main'+'tained'='MAINTAINED'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for maintained that I've seen before include "being kept going" , "Insisted" , "Sustained" , "Kept up (level)" , "Declared; supported" .)