Submarine Commander difficulty and no time limit

[Tangentg]

I always enjoyed Submarine Commander on the Atari 2600 but I was always dissatisfied that the game essentially runs on a timer. Would it be possible to make the game harder? I always set the game to the most difficult game variation but even so I never really get hit. I was wondering if it was possible to ramp up the difficulty (a lot more) and essentially make the game run on lives or health (which only gets depleted if you're hit) rather than the time/fuel limit.