To go a little further........
There are several little "issues".
The Nr indicator is very small and may be difficult to interpret exactly where the RPM is.
Nr is not displayed on the VEMD.
The blades do not like LOW Nr repetitively and were never designed to be subjected to LOW Nr.
Depending on the technique if the throttles are rolled on entry you better be sure that when you return the engines to NORMAL that the throttles are not moved past the N position.
Only a rumour but I heard that the German Army managed to get one to 124% Nr recently.
Why would you want to use a 135 for training in the first place - there are so many things you just could not demonstrate to a student.