I just got a URC R50 and Im looking to program discrete codes to the macros. I was able to get discrete codes on my old MX-500 via the Radio Shack 15-2103 all-in-one remote.

Is this method still used? The pioneer website only shows 4 digit alpha numeric and a long hex code. Can I still program discretes for the tv via a 3 digit IR code?

You didn't mention which model of Pioneer you have, so this may not be completely accurate. If your plasma uses only 4 digit hexadecimal numbers for functions, and not 2 sets of 4 digit numbers (e.g. AA5A+AF7A), then your 2103 should work.
Presumably the 4 digit numbers start with AA (which is 170 in decimal notation).
If so, use TV 0166 as the setup code. Then, for example, to send Discrete On (AA1A), which is device 170, function 26, you would send the EFC 247.

Press Setup briefly and then enter 247. When you enter the 7, the remote will send the signal.

Discrete On 247
Off 251

Probably the discrete inputs are already built-in on the numeral keys. If not,
input 1 058
input 2 054
input 3 102
input 4 238
input 5 011
or
Input 4 246
Input 5 168
Input 6 106
Input 7 052
Input 8 123
Input 9 246