Jewel I perhaps must change (8)
I believe the answer is:
sapphire
'jewel' is the definition.
(I know that sapphire is a type of jewel)
'i perhaps must change' is the wordplay.
'must change' indicates anagramming the letters (I've seen this in other clues).
'i'+'perhaps'='iperhaps'
'iperhaps' with letters rearranged gives 'SAPPHIRE'.
(Other definitions for sapphire that I've seen before include "Blue gem" , "Deep blue - precious stone" , "sparkler" , "His paper can be turned into a jewel" , "Birthstone for September" .)