Hey jedensmore, hey all,
as you already have pointed out, a switch on the output of the VFD, which means between VFD and spindle, is strictly prohibitive and I have never seen a VFD manual that does not warn about it (however poorly it may be explained or illustrated in cheap Chinese manuals).
Regarding the input side of VFD, in front of the VFD, usual setups have a) a MCCB, b) a magnetic contator to prevent the VFD from starting the spindle after a power failure (can also be prevented in the settings of the VFD) and c) a power switch (often a cam switch), which should have a warning not to turn off the appliance when the spindle is in operation. This can also damage the VFD, as the spindle that is still running immediately acts as an induction generator when it becomes powerless and feeds the current back into the VFD. This warning should also be in every VFD manual (it is in mine). The only correct way to stop a running spindle is the RUN/STOP command (on front panel, or as command via ModBus, or as a switch on an Intelligent Input that has been set to the Run/Stop function). The updated IEC 60204-1 standard explicitly states that the activation of the STOP function of a VFD may be regarded as a category 0 stop. That means “Safe Torque Off” (STO), the spindle is made powerless and therefore cannot exert any torque. This means in this state you can safely take your wrenches and change the bit, you don’t need to power the VFD off.