How to pass a value to a DLL of a custom action

Question

This is not an answer to my question because it does not explain (in all three answers) how to deal with incompatibility of @Property and @BinaryKey. Moreover it answers to the "reverse" question: How to retrieve the property not how to "put" it.

I have created a C++ program that replaces in the given file one string by another.

I try to call it from a WiX installer:

                    <Directory Id="ConfigDir" Name="configs">
                        <Directory Id="GenesisDir" Name="genesis" />
                    </Directory>
    ...
    <Binary Id="SetupDLLId" SourceFile="windows\custom.dll" />
    <CustomAction
        Id="SubstituteString"
        BinaryKey="SetupDLLId"
        DllEntry="MyCustomAction"
        Execute="deferred"
        Return="check" 
        Property="[ConfigDir]config.cfg;[GenesisDir]" />

    <InstallExecuteSequence>
        <Custom Action="SubstituteString" Before="InstallFinalize" Property="Subst" />
    </InstallExecuteSequence>

but something does not work (WiX tools compilation fails). I don't know which attribute to use in place of erroneous Property.

C:\blockchain-installer\windows\my.wxs(96) : error CNDL0022 : The CustomAction/@Property attribute cannot coexist with a previously specified attribute on this element.  The CustomAction element may only have one of the following source attributes specified at a time: BinaryKey, Directory, FileKey, Property, or Script.
C:\blockchain-installer\windows\my.wxs(105) : error CNDL0004 : The Custom element contains an unexpected attribute 'Property'.

C++ source:

#include <windows.h>
#include <cstdlib>
#include <stdio>

extern "C" _declspec(dllexport) UINT __stdcall MyCustomAction(MSIHANDLE hInstall);

extern "C" UINT __stdcall MyCustomAction(MSIHANDLE hInstall)
{   
    DWORD dwSize=0;
    UINT ret1 = MsiGetProperty(hInstaller, TEXT("CustomActionData"), TEXT(""), &dwSize);
    if(ret1 != ERROR_MORE_DATA && ret1 != ERROR_SUCCESS) {
        std::exit(1);
    }
    ++dwSize; // include the terminating null character
    TCHAR data = new TCHAR[dwSize];
    UINT ret2 = MsiGetProperty(hInstaller, TEXT("CustomActionData"), data, &dwSize);
    if(ret2 != ERROR_SUCCESS) {
        std::exit(1);
    }

    size_t pos = data.find(';');
    std::string filename = data.substr(0, pos);
    std::string directory = data.substr(pos + 1);
    std::string content;

    std::ifstream file(filename);
    std::string contents((std::istreambuf_iterator<char>(file)), (std::istreambuf_iterator<char>()));

    std::string needle = "%GenesisDir%";
    size_t pos2 = contents.find(needle);
    contents.replace(pos2, needle.length(), directory);

    std::ofstream file2(filename);
    file2 << contents << std::flush;

    delete[] data;
    return ERROR_SUCCESS;
}

Please, describe the correct code in details.

If it is impossible to do with DLL, then guide how to do it with .exe instead.