SWIFT ISO 15022 - Code POSS Financial acronyms The entire acronym collection of this site is now also available offline with this new app for iPhone and iPad. Meaning Change of Possession: Change in the possession or ownership of the financial instrument. Usages Message type Field number Tag MT500 (Instruction to Register) 14 22F (Indicator) MT501 (Confirmation of Registration or Modification) 14 22F (Indicator)