#! perl
use strict;
use warnings;
use Data::Dump;
use YAML::XS;

my $hash = { Fred => 'Wilma', Frederick => 'Mary', Barney => 'Fred' };
my $yaml =   Dump $hash;
   $yaml =~  s/\bFred\b/FRED/;
   $hash =   Load $yaml;
dd $hash;