For error/view, there are quite a few settings in site.ini that might fit the bill for your needs wrt. customized error management. It's a bit hard to understand what they do, so I advice to simply experiment.
As for taking control over an existing module/view: iirc it is possible, using url aliases. Not sure it will work for things that are accessed via internal module redirects though...
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@Mark: it's only working for classes. The reason of this thread. But thanks anyway. ;)
@Heath: probably the easiest way for me here... But I dislike to patch the kernel.
@Gaetano: I read few threads about the url alias option, but I have no idea how to use it for kernel/errors issues with "undefined" URLs like kernel 20 errors.