This is not a modification really. It's just an idea of using your expression pedal output as a 'line out' for your L100. Note that none of the modifications done to the power amp (e.g. Zener Overdrive) will be heard on this setting.
Simply pull out the white plug that goes to the expression pedal from the power amp unit and that's it. You can buy a RCA to jack adaptor and do with the sound whatever you like. I put my L122 through some multi-effect pedal and Marshall keyboard amplifier. This is the real Jon Lord sound.
If you wish you can buy RCA divider and use internal amplifier and speakers as well but I donít see the point of doing that.
If you don't want to bypass the power amp and use the speaker wires instead, you need to follow these instructions: