About the position to substitute (7)
I believe the answer is:
replace
'to substitute' is the definition.
(synonyms)
'about the position' is the wordplay.
'about' becomes 're' (regarding).
'the position' becomes 'place' (place is a kind of position).
're'+'place'='REPLACE'
(Other definitions for replace that I've seen before include "Provide a substitute for" , "Put back or substitute" , "Put something back where it belongs" , "Substitute, supplant" , "succeed" .)