Allowance for one's PIN having changed (7)
I believe the answer is:
pension
'allowance' is the definition.
(thesaurus)
'one's pin having changed' is the wordplay.
'having changed' indicates anagramming the letters.
'ones'+'pin'='onespin'
'onespin' with letters rearranged gives 'PENSION'.
'for' is the link.
(Other definitions for pension that I've seen before include "support for the elderly" , "Bed and breakfast or small hotel in France" , "what oldies may have earned" , "Retired person's allowance" , "residence abroad" .)