use warnings;
use strict;

my $path = "XX.YY.ZZ";
my $s    = "(ABC | (~dEf & hIJ)) & ~LMn";
$s =~ s/([a-z]+)/$path.$1/gi;
print "$s\n";

__END__

(XX.YY.ZZ.ABC | (~XX.YY.ZZ.dEf & XX.YY.ZZ.hIJ)) & ~XX.YY.ZZ.LMn