Older MRC Prodigy Advance

I purchased my Prodigy Advance system many years ago.  I recently attempted to install and program a decoder into a standard DC locomotive but could not access functions 20-28 before I realized the “shift” button didn’t go that high.  I see the Advance2 system does go that high, and I see that the throttles are available for separate sale.  Here’s the question:  can I access functions 20-28 by replacing ONLY the old throttle with the newer throttle from the Advance 2, or do I need to purchase the whole system?  Note the different labeling of the shift button on the lower right with the old controller on top vs the labeling on the newer controller below it.