Quick update: When I last posted here, the state of affairs was such:
1. Segfault when using this program from the /sbin/preinit point in the boot process.
2. Unable to set/read R&D mode on an N900 that has NEVER had R&D mode set before in it's lifetime (but at least it no longer segfaulted in such cases, as was the case in the last precompiled binary I posted on this thread).

I have just gotten back to this yesterday, and as of earlier this morning, I was able to turn on R&D mode on the N900 I had which, until that point, never had R&D mode enabled on it. Rebooted to confirm it worked (it did), and then turned R&D mode off and rebooted to confirm that worked. Success. So issue 2 is near as I can tell, fixed, but still need to figure out the cause for issue 1. But I consider this a major achievement, in that it makes this FAR more useable for it's intended usecase of letting people turn on R&D Mode on-device (and if you depend on flasher to do it for the 'first time', that's a large amount of scenarios where this tool would be useless).

I will update the source in the first post once I've cleaned up the logic of the code better (and once I get around to it after that). Right now I just took a gamble that you could write to the cal area even if the other two functions for reading the contents of the libcal area return 'false's, and just commented out the return statements in those if blocks - this seems to work just fine, but as a result, the code needs rearranging, me thinks.