This isn't a Perl solution, but I'd just hook some
custom elisp functions up to cperl-mode for this. The
advantage of this approach is that the functions can look
at the syntax information in the text properties, so that
you can for example choose not to alter the whitespace
inside strings or comments, without writing any code to
parse where strings and comments begin or end -- one less
wheel to reinvent. The disadvantage is that you have to
know elisp, in addition to Perl.
"In adjectives, with the addition of inflectional endings, a changeable long vowel (Qamets or Tsere) in an open, propretonic syllable will reduce to Vocal Shewa. This type of change occurs when the open, pretonic syllable of the masculine singular adjective becomes propretonic with the addition of inflectional endings."
— Pratico & Van Pelt, BBHG, p68