Hi Chris;
As Marco and Matt point out - you can install PB2017Rx alongside PB 12.6 with no issues.
However, there is one "gotcha" and that is in the area of .NET Web Services. PB utilizes a few DLL's in its "Shared" folder for this venture that are not release number named (for example: LIBxxxxxx and SSxxxxxxx DLL's). The one that will kill your Web Service execution is ssleay32.dll. Mixing this DLL from PB 12.6 at run time with a PB2017 WS will fault the execution. Also, using the same DLL from PB2017 with a 12.6 WS execution will fault its execution.
So the only area to be aware of when both IDE's are installed on the same machine is the Web Service feature. I handle this by changing the System Path of the O/S when working on PB 12.6 projects vs PB2017 ones by placing the related SHARE folder higher in the system path that matches the PB version I am using when deploying & testing web service components. I have been doing this trick since PB 11.0 => 2017 and it works 100% for me.
HTH
Regards ... Chris
Top-notch advise.
.m