I find it's good practice to "capture" your capture variables immediately after a match even when you know for sure you will never be doing any further regex matching within that scope:

if ($macs[1] =~ /(\S{17})\|(\S{17})/) {
    my ($mac1, $mac2) = ($1, $2);
    ...
    $mac1 =~ s/.../etc/g;
    $mac2 =~ s/as/needed/g;
    ...
    do_something_with($mac1, $mac2);
    ...
    }
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Just a thought. Since you are only switching one character you could use y/// or tr/// instead of s/// and you would not overwrite your match/capture variables. Like: tr/:/-/.