How to define my own show page for MUI_UNPAGE_INSTFILES?

I can define my own show page for MUI_PAGE_INSTFILES like this:

!define MUI_PAGE_CUSTOMFUNCTION_SHOW MyinstShow
Function MyInstShow
....
FunctionEnd
!insertmacro MUI_PAGE_INSTFILES
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But how to define my own show page for MUI_UNPAGE_INSTFILES?
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!define "???" MyUninstShow
Function MyUninstShow
....
FunctionEnd
!insertmacro MUI_UNPAGE_INSTFILES
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How to define "Function .onGUIInit" in my own script to ignore the "Function .onGUIInit" in System.nsh ?

FunctionEnd

1. Same, MUI_PAGE_CUSTOMFUNCTION_SHOW.
2. !define MUI_CUSTOMFUNCTION_GUIINIT myGUIInit.

Stu

Thank you.I understand.
!define MUI_PAGE_CUSTOMFUNCTION_SHOW un.MyUninstShow