Excel is almost certain to change (7)
I believe the answer is:
'excel' is the definition.
(I know that excel can be written as surpass)
'almost certain to change' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'certain' becomes 'sure' (synonyms).
'to change' becomes 'pass' (passing is a kind of changing).
'sure' with its last letter taken off is 'sur'.
'is' is the link.
(Other definitions for surpass that I've seen before include "supply best" , "Outstrip" , "eclipse visible" , "Transcend" , "Be better than (another)" .)