Note if you modify a vehicle system to non-factory, then all of a sudden all those Mercedes repair shops out there no longer have documentation, test equipment, test procedures, or the troubleshooting knowledge to fix your modified vehicle!

So if something stops working, you will be on your own to troubleshoot and fix it. Best you totally understand these systems so you can do that.

If you just want to tinker with the adjustments on a fuel injection system for any vehicle - does not matter if Mercedes or not, then might want to poke around the following site which has free "tuning" software for certain 90's vehicles (and buy one of those vehicles to experiment with).

With that you would modify the programming on the vehicle's computer chip and plug it into the vehicle's computer. If your modified programming did not work, you could re-install the factory chip. Or if you need to take it to a mechanic for troubleshooting, you could reinstall the factory chip.

Tuning software...
TunerPro and TunerPro RT - Professional Automobile Tuning Software

Interesting 90's GM free vehicle computer reading software...
WinALDL - 160 baud ALDL reader