FREEWARE productsInno SetupCompiler ,IsTool  and My Inno Setup Extensions 3 are highly customizable and great RhinoScript Companion

You can read/write from the registry at setup run time and many, many other useful options ...
Just an example: Read Rhino installed path from the registry:
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DefaultDirName={reg:HKLM\SOFTWARE\McNeel\Rhinoceros\3.0\{reg:HKLM\SOFTWARE\McNeel\Rhinoceros\3.0\,MostRecent}\Install\,InstallPath}\Plug-ins\MYAPP_DIR

Write to the registry a new Rhino alias:
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Root: HKCU; SubKey: Software\McNeel\Rhinoceros\3.0\Scheme: Default\Options\AliasList; ValueName: EC; ValueType: string; ValueData: !Run {app}\MYAPP.EXE; Flags: deletevalue uninsdeletevalue

With the My Inno Setup Extensions 3 we can include some PASCAL scripts to do some calculation or anything on setup run-time. How it looks like in the real life?:

Let say we want to include our custom workspace(ws3) with our VBS script or VB.exe. So,( from my "research") we need to get number of workspaces (Count) already installed, located in here: HKCU,'Software\McNeel\Rhinoceros\3.0\Scheme: Default\RhinoToolBarManager\Count
once we have it, we need to create a new key with the value of Count and then increment Count for one and  write it to the registry. here is the PASCAL script to do so:
[Code]
var
StartInstall: Boolean; //This function will be invoked when user click on the INSTALL button
function GetCount():Boolean;
 var RHCount:String;
 var new_RHCount:String;
begin
 RegQueryStringValue(HKCU,'Software\McNeel\Rhinoceros\3.0\Scheme: Default\RhinoToolBarManager','Count',RHCount);
 new_RHCount := IntToStr(StrToInt(RHCount) + 1);
 RegWriteStringValue (HKCU,'Software\McNeel\Rhinoceros\3.0\Scheme: Default\RhinoToolBarManager', 'Count',new_RHCount );
 Result := True;
end;

function GetNewCount(S:String):String;
 var RHCount:String;
 var new_RHCount:String;
begin
 RegQueryStringValue(HKCU,'Software\McNeel\Rhinoceros\3.0\Scheme: Default\RhinoToolBarManager','Count',RHCount);
 new_RHCount := IntToStr(StrToInt(RHCount) - 1);
 Result := new_RHCount;
end;

so the GetNewCount we'll call in our registry section
[Registry]
Root: HKCU; Subkey: Software\McNeel\Rhinoceros\3.0\Scheme: Default\RhinoToolBarManager; ValueType: string; ValueName: {code:GetNewCount}; ValueData: {app}\MYWORKSPACE.ws3

Download Rhino-Inno install script