DWORD sizeOf =0;
HGLOBAL hSomeResource =NULL;
LPVOID  pvSomeResourceData = NULL;
HRSRC hResource = FindResourceA(GetModuleHandleA(NULL), "test", RT_STRING);
if (NULL == hResource)
{
  // TODO throw "cann't find resource"
}
else
{
  sizeOf = SizeofResource(GetModuleHandleA(NULL), hResource);
  hSomeResource = LoadResource(GetModuleHandleA(NULL), hResource);
  if ((hSomeResource) &&(sizeOf))
  {
    pvSomeResourceData = LockResource(hSomeResource);
    char *buf = malloc(sizeOf);
    if (!buf)
    {
       // todo throw "cann't allocate memory"
    }
    else 
    {
      unsigned long add_len = strlen("test");
      MoveMemory(pvSomeResourceData, buf, sizeOf);
      if ((sizeOf >= (sizeOf+add_len)) || (add_len >= (sizeOf+add_len)))
      {
    // todo throw "invalid internal params"
      }
      else
      {
        buf = realloc(buf, sizeOf + add_len);
   sprintf_s(buf,sizeOf+add_len,"%s","test");
   memcpy(buf+add_len, pvSomeResourceData, sizeOf);
   if (NULL!=(pvSomeResourceData = malloc(sizeOf + add_len)))
   {
      MoveMemory(buf, 
                      data_from_file, 
                      ((sizeOf + add_len)>=sizeof(Buffer)) ? sizeof(Buffer) : (sizeof+add_len));
      free(pvSomeResourceData);
        }
      }
    }
  }
}