We have a constantly changing list of IPs that needs to be filtered out of google analytics, is there some API, or way to fetch the list of IPs to be included in a Google Analytics filter?
Sadly, no , although this would be a great feature though. The best thing you can do is block ranges of IP, you can do this with the following format:-
Google have an IP range generation tool to help you out with this.
You can now do this as part of their Google Analytics Management API.
Example in Python