Here is a romlog, if you want to have a look. For me it's not that important, since the set_config_value()-method works. Don't know how many people have a SX200IS out there, it's not the newest cam.
If a very simple function like set_raw_nr crashes, there is probably a major problem somewhere, so we would like to fix it.
Did it crash when you called set_raw_nr, or when you tried to shoot after setting it? It looks like the crash in you romlog happened shortly after shooting.
What value did you try to set?
Is the crash repeatable?
From the romlog
ASSERT!! FocalLengthConverter.c Line 146
Occured Time 2014:01:02 01:23:49
Task ID: 48889891
Task name: CreateHeader0
This does not appear to be in any CHDK task. That doesn't mean CHDK didn't cause it, but it doesn't seem obviously related to set_raw_nr. I would guess CreateHeader0 has something to do with creating the exif.
Does the time stamp: 2014:01:02 01:23:49 seem like the time this crash happened? Sometimes a crash doesn't generate a romlog, in which case the romlog could be from some other crash. The time is from the camera clock, so if it isn't set correctly take that into account.