Changing AccessorDecl ParameterList during semantics pass

I’m attempting SR-5982 <Issues · apple/swift-issues · GitHub, and so far have been able to check for whenever oldValue is unused during the code synthesis, once the AST has been generated.
But during parsing the oldValue parameter is always added to the didSet function, and at this stage I’m not sure if it’s possible to walk or check the body for any references to the parameter.
Is it possible to modify the ParameterList of an AccessorDecl in swiftSema, specifically in CodeSynthesis.cpp, so I can call the didSet function without the oldValue parameter whenever it is not needed?