Patrick ~
I'm not an insurance 'expert' but I sold life insurance at one point in my career and my wife was a claims supervisor for a major insurance company, so I do have a working knowledge of the business.
My suggestion would be that you not risk trying to apply for more life insurance at this point. Although the '5 year' question can be answered honestly ('no') the application could ask about any surgeries you've had, without a specific time frame, forcing you to state your AN surgery (lying invalidates the policy) and possibly being denied coverage or at least having your premium jacked up. Because you took out your current policy before your AN diagnosis, it should cover you even if you died from something AN-related, although that is extremely unlikely to happen.
In the future, if you chose to take out a different life insurance policy (upon retirement) the '5-year' question will likely be asked. As long as the application doesn't ask about any surgeries - without a specific time-frame - you'll be fine. Should the AN surgery have to be revealed, it could raise your premium, but I doubt it would cause your application to be flatly denied. This is life insurance, not 'health'/medical insurance and there is a different standard for the underwriting. However, be aware that with life insurance, the higher the benefit amount, the more stringent the underwriting.
Jim