In emergency driver may use this, for a change (5,4)
I believe the answer is:
spare tyre
'in emergency driver' is the definition.
The definition suggests a singular noun which matches the answer.
'use this for a change' is the wordplay.
'use' becomes 'spare' (sparing is a kind of using).
'this for a change' becomes 'tyre' (I can't explain this - if you can you should believe this answer much more).
'spare'+'tyre'='SPARE TYRE'
'may' acts as a link.
Can you help me to learn more?
(Other definitions for spare tyre that I've seen before include "evidence of overindulgence" , "Roll of fat around the waist, like car part" , "large corporation" , "Fat around the midriff?" , "It's carried in case of a blow-out" .)