You can do something along these lines but there's a few steps:
First, you need to break out those requests from the ones that are not failing through a request naming rule. You could decide what makes the most sense but the goal is to break these requests out into a separate request when your conditions (url and error codes) are met.
After this as these requests come in they will end up in this new named request. You can then mute this request and it will be excluded from error rates and alerting etc...