It isn't impossible. It's a pretty straight forward modification of the php files.
When I used IP, I had to manually edit the php all the time.
If you don't update often it's a great solution, but if you like to keep stuff up to date as you should, it's painful.
Forums and other websites get cracked and broken into all the time. By far one of the most common reasons I see for such incidents is that the site owners were using an old version of their software in the interest of preventing anything from breaking. Given, IP.Board is much more secure than most forum platforms, but each update includes many useful bug fixes and sometimes a security fix as well, so I tend to prioritize the installation of updates.
The third generation of the IPS framework has a hooks system designed to avoid the pain of manual code edits, but creating a hook to override the default functionality of the swear filter would require a developer who is familiar with the platform (that is, if it is even possible to hook into the swear filter). There are also performance considerations to take into account as well, considering that IPB is designed to cache posts in fully rendered, raw HTML. If each user could choose whether to see a filtered or non-filtered version of a post, this would either require the system to be modified to cache two different copies of the post or posts would need to be parsed and filtered on-demand.
These are just a few considerations to keep in mind before I start hacking away at raw PHP.