Altering in development becomes intrinsic (8)
I believe the answer is:
integral
'intrinsic' is the definition.
('integral' can be similar in meaning to 'intrinsic')
'altering in development' is the wordplay.
'in development' indicates anagramming the letters.
'altering' with letters rearranged gives 'INTEGRAL'.
'becomes' is the link.
(Other definitions for integral that I've seen before include "Belonging as an essential part" , "Triangle being essential" , "'Inherent, inbuilt (8)'" , "using no fractions" , "Triangle (anag)" .)