In order to swap the CDs, it is necessary to prevent the Saturn from returning to the main menu even if the lid is opened.
If you have a gray Saturn (the model with the access light), if disposable chopsticks are shoved into the left hole on the CD drive the lid will be "closed".
The white Saturn (without the access light) is slightly more difficult because the lid switch is not accessible from the outside.
There are these methods:
If you can trick the lid switch in some way, let's start LO.
Insert the LO disc, and turn on the power with the lid open.
First, after reading the track information, the pickup moves to the outside of the disc, making a buzzing noise.
At this time, exchange the LO disc and an original Saturn disc. Since the protection check is retried several times, you can change the disc slowly without any issues.
After checking the outer ring of the disc, the pickup returns to the center of the disc. Please quickly switch to LO here.
The timing is fairly tricky. You'll be successful if you swap quickly at the moment the pickup returns to the disc's center.
If the original CD is pulled out early, the pickup will retry the security check. If you take too long inserting LO, the CD will not spin.
When it works, the SEGA logo will appear on the screen and LO will start up.
Since the time window to re-insert the LO disc is small, first observe normal software running on the Saturn several times, Insert LO right before the SEGA logo would normally appear.
With my white Saturn, I fixed the lid switch and I think that this is the easiest method to start LO.
TL note: If you have a Model 1 Saturn, here's an easier way to do the swap trick:
1. Insert your copy of LimitOver, wait for the access light to stop blinking.
2. When the access light stops blinking, swap LO for a real Saturn disc.
3. The access light will blink 3 times when checking the outer ring. After this, swap the discs again and you should be running LimitOver.