Modify system function in 50g

[Han]

It depends on what you want to replace. If the system object that you would like to replace happens to be a library, then you could try to modify the ROMPTAB and swap the tables for the built-in routines with your replacement library. One example of this is SpeedUI.

If you wish to create a new System Outer Loop (SOL) there are plenty of examples of these on hpcalc.org's archive.

ROM viewers are also available. Many programs such as Nosy seem to be outdated past the HP49G (i.e. new opcodes for the HP50G are not supported). If you are familiar with the HP style, then Jazz 50G may be useful to you (integrated editor/ROM viewer) and was updated to work with the last firmware revision 2.15.