Part 1:Ah cool, I wasnt sure so good thing I posted
I have a few 650's so if you want I can help test.
Part 2: Polycom Version [0.7.5]
If you look at the spip_sip.cfg it is identical (according to winmerge) to the {$mac}_{$ext}_sip_custom.cfg. I dont have to remove it each time. I edited the template (the $mac.cfg) for polycom from Advanced -> Product Options and commented out the spip_sip.cfg. So going forward the file spip_sip.cfg is created but the phone wont look for it.
I didnt test it but is there any purpose for both the spip_sip.cfg and {$mac}_{$ext}_sip_custom.cfg files for the other polycom phones?
Part 3:
I meant it as you described it, to delete the config files. Once this is implemented a feature that I could see useful is to create a blank phone file with a dead, disabled or terminated extension (allow that extension to be loaded multiple times) that when that phone registers it would be dead in a sense.
I'll see if I can get some free time during the week on a test system or by the weekend and see if I can try to help implement this and the blanking out feature.