Unchanging, those full of beans, say in early part of tennis match? (3,2,5)
I believe the answer is:
set in stone
'unchanging' is the definition.
'those full of beans say in early part of tennis match?' is the wordplay.
'those full of beans say' becomes 'tins' (as in tins of beans).
'in' means one lot of letters goes inside another.
'early part of tennis match?' becomes 'setone' (set one or the first set in a tennis match).
'tins' going into 'setone' is 'SET IN STONE'.
(Other definitions for set in stone that I've seen before include "as Excalibur?" , "Fixed and unalterable" , "As inflexible" .)