Some games of short tennis arranged and unlikely to be changed (3,2,5)
I believe the answer is:
set in stone
'unlikely to be changed' is the definition.
'some games of short tennis arranged' is the wordplay.
'some games' becomes 'set' (I have seen 'games of tennis' mean 'set' so perhaps 'games' could also mean 'set').
'short' means to remove the last letter.
'arranged' indicates an anagram.
'of' with its final letter taken off is 'o'.
'o'+'tennis'='otennis'
'otennis' anagrammed gives 'instone'.
'set'+'instone'='SET IN STONE'
'and' is the link.
(Other definitions for set in stone that I've seen before include "as Excalibur?" , "Fixed and unalterable" , "As inflexible" .)