Overriding existing Signature Help with my own Signature Help

I'm building an extension for improved signature help for compiler intrinsics in c++. It works perfectly for intrinsics that are not supported (AVX512 etc); however, the existing signature help for supported intrinsics interferes with my new signature help. The Walkthrough on displaying signature help does not address this issue.

Questions:

1] Is there a way to order signature help command handlers such that my signature help is processed before the default one. I have:

[Export(typeof(IVsTextViewCreationListener))]
[Name("Intrinsic Signature Help controller")]
[TextViewRole(PredefinedTextViewRoles.Editable)]
[Order(Before = "default")]
[ContentType("C/C++")]
internal sealed class IntrSignHelpCommandProvider : IVsTextViewCreationListener

2] How do you override existing signature help functionality? The existing signature help session changes the ITextBuffer by adding a close parenthesis, which triggers another signature help session. Can someone point me to source code that handles more complex situations such as the one described above?

Regards, Henk-Jan.