This is tricky. You'd have to do it as a component parameter, since the part could have any number of simplified reps, right? You can definitely make a repeat region that shows the component parameter SIMPREP if it exists, and if it doesn't, show the part number. But you'd still have to set the component parameter for each part that uses a simprep manually, and it wouldn't update. If you want it automatic, my guess is you need some Web.Link / Jlink / other Toolkit program to do this.
