You want to install multiple versions of the software on you PC, but are worried about the ability to go back and run previous versions. This page explains the installation procedure, and hopefully can help you understand how to safely install multiple versions, and go back to previous versions.
When installing a demo, file the filename is prefixed with "Demo", as shown below.
Following Step 4 of the installing Version 3.41, Build C the following files two simulators are installed. Note that files ETpuSimulator.exe and ETpuSimulatorV3_41C.exe are identical. Why is that? Well, file ETpuSimulator.exe is the active file, such that this is the simulator version that will be used when you launch the simulator either by double clicking on a project file from within explorer. Whereas file ETpuSimulatorV3_41C.exe is the "legacy" copy that will never get overwritten such that you should be able to return to it.
Let's say a little while later you install Version 3.42, Build F, what file gets written? Well, it overwrites the existing file ETpuSimulator.exe to this version because this is the active version. But it ALSO creates a new legacy file for this latest version called, ETpuSimulatorV3_42F.exe, as shown below.
So here is the beaf. How does one return to a previous version? Do the following copy:
copy "c:\Program Files\ASH WARE\eTPU Simulator\ETpuSimulatorV3_41C.exe" "c:\Program Files\ASH WARE\eTPU Simulator\ETpuSimulator.exe"