You could extend the SNMP class to add your needed code to the mib loading method and then SUPER:: it. This would probably be more work than adding the few lines you need.

Also, you probably ought to avoid that `ls` construction and go with readdir ...

$root="/usr/local/share/snmp/mibs/TEMP";
opendir(DIR, $root) || die "can't opendir $root: $!";
map { &SNMP::addMibDirs($_); } 
          grep { ! /^\./ && -d "$root/$_" } readdir(DIR);
closedir DIR;
[download]

Which also avoids accidentally trying to add files as MibDirs and is safer and more portable.