Change US postal codes (CA) to AP stylebook abbreviations (Calif.) in bibliography (biblatex)

Question

My .bib file is using US postal codes as abbreviations for US states (CA and MA for California and Massachusetts). For a paper I'm writing, these need to be changed to abbreviations such as Calif. and Mass. (cf. Wikipedia).

I'd prefer not to change my .bib file, but instead include a command in my preamble that says "When the entry LOCATION in the .bib file has strings such as , CA, , MA, etc., then substitute these with , Calif., , Mass., etc.". (I've added a comma plus space before the strings to be absolutely certain that it doesn't catch any two-letter strings that aren't US states - not that I know right now what that would be, but just in case).

MWE:

\documentclass{article}
\usepackage[style=authoryear]{biblatex}
\begin{filecontents}{\jobname.bib}
@BOOK{lehiste1970,
    AUTHOR = "Ilse Lehiste",
    TITLE = "Suprasegmentals",
    YEAR = "1970",
    LOCATION = "Cambridge, MA",
    PUBLISHER = "The M.I.T. Press"}
\end{filecontents}
\addbibresource{\jobname.bib}
\begin{document}
\nocite{lehiste1970}
\printbibliography
\end{document}

This should read

Lehiste, Ilse (1970). Suprasegmentals. Cambridge, Mass.: The M.I.T. Press.

Answer 1

Here's a proof of concept.

\begin{filecontents}{\jobname.bib}
@BOOK{lehiste1970,
    AUTHOR = "Ilse Lehiste",
    TITLE = "Suprasegmentals",
    YEAR = "1970",
    LOCATION = "Cambridge, MA",
    PUBLISHER = "The M.I.T. Press"}
@BOOK{mehiste1970,
    AUTHOR = "Ilse Mehiste",
    TITLE = "Suprasegmentals",
    YEAR = "1970",
    LOCATION = "San Francisco, CA",
    PUBLISHER = "The California Press"}
\end{filecontents}

\documentclass{article}
\usepackage[style=authoryear]{biblatex}

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \step[fieldsource=location,
        match=\regexp{,\s*(MA|CA)},
        replace=\regexp{,~\\State\{$1\}}]
    }
  }
}
\addbibresource{\jobname.bib}
\def\State#1{\csname State#1\endcsname}
\def\StateMA{Mass.}
\def\StateCA{Calif.}

\begin{document}
\nocite{*}
\printbibliography
\end{document}

Instead of replacing MA with Mass. I think it's better to replace it with \State{MA}, so that a definition can be given (and modified at will).