In the code you have the "5000 0072 0000 0001" just means the signal is RC5. The next 0000 is the device number, so in the .irp file you need to make sure you have DEVICE=0.

The 0038 is the function number, but it is in hex. MakeHex's input for function numbers is in decimal, and by default its output of function numbers is also decimal. See its readme for getting function output in hex, or translate the function numbers you want to decimal before using MakeHex.

0038 hex is 56 decimal.

Assuming you want several functions translated, it's easiest to leave the full range specified in the Function line of the .irp, then find the ones you want in the .hex file.