[aguml]

Así quedaría mi función de reemplazo:

Código PHP:

bool __fastcall TForm1::Replace(WideString path, BYTE *original, SIZE_T sizeOriginal, BYTE *reemplazo, SIZE_T sizeReemplazo, bool overwrite)
{
    std::auto_ptr<TMemoryStream> pmsOriginal(new TMemoryStream);
    std::auto_ptr<TMemoryStream> pmsNuevo(new TMemoryStream);

    char c;
    int i;
    long pos = 0;
    bool founded = false;
    
    try
    {
        pmsOriginal->LoadFromFile(path);
        do{
            pmsOriginal->Read(&c,1);
            if(pmsOriginal->Position + sizeOriginal <= pmsOriginal->Size){
                if(c == original[0]){
                    pos = pms->Position - 1;
                    for(i=1; i <= sizeOriginal; ++i){
                        pmsOriginal->Read(&c,1);
                        if(c != original[i])
                            break;
                    }
                    if(i == sizeOriginal){
                        pmsNuevo->Write(reemplazo,sizeReemplazo);
                        founded = true;
                    }
                    else
                    {
                        pmsOriginal->Seek(pos,soBeginning);
                    }
                    pmsOriginal->Read(&c,1);

                }
            }
            pmsNuevo->Write(&c,1);
        }while(pmsOriginal->Position < pmsOriginal->Size);

        if(founded){
            WideString pathDestino;
            if(overwrite)
                pathDestino = path;
            else
                pathDestino = path.SubString(1,path.Length() - ExtractFileExt(path).Length()) + "_copia" + ExtractFileExt(path);
            pmsNuevo->SaveToFile(pathDestino);
        }
    }
    catch(...)
    {
        ShowMessage("Streaming error.");
    }
    return founded;
} 


Si piensas que debo cambiar algo soy todo oídos.