You can replace them. I forget the details on how I did it, but I recall doing this for a popular first person star wars game at the time. I replaced the DPMI runtime with a different one and the level load times skyrocketed in speed. My suspicion at the time was that the runtime included switched to real mode to do disk transfers but the other perhaps talked directly to the IDE hard disk staying in protected mode? Not sure, but it was very, very fast with I/O. I was pretty happy with my hack at the time.