use warnings;
use strict;

while (<DATA>) {
    s/(Z=)(\d+)/$1 . $2*4/eg;
    my $i = 1;
    s/\b(XP)\b/$1 . ' (' . $i++ . ')'/eg;
    print;
}

__DATA__
Z=1 Z=2
Z=3
foo XP bar XP boo