File handling in RouterOS is very basic, no cat-like commands. Aside from that, the file is 80+KB. That is a problem because inside RouterOS there is a 4KB limit for reading / writing files: http://forum.mikrotik.com/t/save-export-to-variable/36882/3
I would do something like this: Download the file locally to PC, use other software to remove the # lines and add correct code, basically make the file into a script. So this:
# last updated 1337878082 (Thu May 24 16:48:02 2012 GMT)
0.0.0.0/8
5.10.0.0/18
223.130.28.0/22
224.0.0.0/3
# eof
would become:
/ip firewall address-list
add address=0.0.0.0/8 list=BlockedList;
add address=5.10.0.0/18 list=BlockedList;
add address=223.130.28.0/22 list=BlockedList;
add address=224.0.0.0/3 list=BlockedList;
Name the new file something.auto.rsc, upload to the router using ftp, and the script will execute automatically. Of course, if the ip already exists, a duplicate will be added, so checking for that would also need to be added to the script.