Indeed, good tip Aoktar! I use it all the time with pre-R21 C4D but a quick warning for anyone trying to run R21 in parallel... It won't work as they've completely disabled that functionality (potential corruption issues with the install folders).
The solution is to copy the R21 folder a couple of times and then you can run those installations separately and in parallel. The downside is that they all act like separate c4d installations so if you update a plugin in one installation you need to update it for all of the instances. A huge downside then is also having less SSD space available :\
If we want the parallel option back I think its best to let Maxon know about that