No it can't be upgraded. Depending on the rebadging there are 2 different jr t's...1 is 6inches and tends to be the newer one which is actually a jrt. There is also a 5inch version made for Norco which used 2002 rebadged dj lowers. Depending on which one you find will determine the price. I believe the jrt pro is 7 inches.

5in jrt - wouldn't pay more than 500cdn
6in jrt - 700ish cdn
7in jrt - 1000 or so

Those are approximates