If you want to blacklist a large list of IP addresses (like the SpamHaus DROP list, or other known-malicious sites, for example) then create a custom IP signature in IME.
Use the Atomic IP engine and specify the destination IP Address. Use a variable for the list of IPs and in that variable you'll put your blocklist.
Whitelists are Event Action Overrides. Just specify the IP and all of the sigs that you want it to be excluded from (including "all")
I have done a ton of work with blacklisting IP's in my 20+ IPS sensors. I have written quite a few scripts to automate the update of the blacklist variables, but that uses Cisco Security Manager (CSM). I looked at scripting this with EXPECT scripts but the CLI for the IPS sensors (plus the fact that I had 20 of them and was using CSM) made it too difficult. If anyone else wants the scripts just let me know. I think I've posted them before though.