FYI it appears you can run multiple installations. I don't know if this is going to cause any problems in future, but I currently have 1.4, 1.4.1 and 1.4.2 all installed on my computer and can run them simultaneously. I've built projects with all versions since having them all installed and haven't noticed any problems so far.
All I did was copy the folders for each older version prior to running the installer, then pasted them back in once the install of the newer version was complete (these are under C:\Program Files (x86)\MoTeC\M1\Build\1.4, C:\Program Files (x86)\MoTeC\M1\Build\1.4.1 and C:\Program Files\MoTeC\M1\Build\1.4.2). I then just made shortcuts to each M1Build.exe file on the desktop and named them appropriately.