I use the PRV and use RPN 0 to adjust pitch bend range for the synth I use. There are many occasions where I too have to increase the pitch bend range from the default of 2. The external synth I use is an SW1000XG, which is basically a S-YXG50 on steroids, so this should also work for the S-YXG50.
Note: Not all synths adhere to this standard. For instance Rapture pro uses a set of NRPN events to control its pitch bend range. It really depends on the synth.
When I select RPN 0 in the PRV, it actually has the name "Pitch Bend Sensitivity" because I am using the instrument definition file for Yamaha XG instruments that is available even if I am using a soft synth.
You can also use standard controllers event to generate RPN events. So, for example, if you want to change the pitch bend range to 3 of a given channel for the S-YXG50, for instance , you would need to put the following controller events in the respective track (in this order)
CC 100 0
CC 101 0
CC 6 3 <------- this would be your pitch bend range
Hope that helps