You can already block a range of IP addresses!
Why not just entering these data to block invalid or local addresses:

0.*.*.*
10.*.*.*
127.*.*.*
172.16.0.0/255.240.0.0
192.168.*.*
224.0.0.0/224.0.0.0

Note there are 2 syntaxes supported to specify a mask, one with stars matching any byte value in the IP, and one that supports an IP mask in dotted notation (needed when the network mask length is not a multiple of 8 bits).

Currently the bit-length notation for masks and and short notations for network addresses are not implemented, so the following is refused:

0/8
10/8
127/8
172.16/12
192.168/16
224/12

If you want to copy paste a lot of addresses, you need to edit your "limewire.props" settings file, and modify the setting of BLACKLISTED_IP_ADDRESSES. If a line is too long, you may wrap it, but don't forget the ";" separator between addresses.