This was pretty long and at least some of it was on topic.
If username changes are causing a volume problem for mods then sure cut it down from 1 month to 2 or 3 months for most people, but I agree a year is excessive.
How about leaving it as is (or 2/3 months) for normal people and if people were banned or something, require a year? That way the ability to change names is a perk for not doing shit that gets you banned?
Should be pretty straightforward to implement since it sounds like all youd need is an extra check in the user name change form for "was user banned in last <x> months?"
I also read someone suggest that bans/things should require contact with the mod team. I dont know how many bans the mod team dish out (maybe that would lead to a volume problem too?) but I actually like the idea a lot: ban timer starts when the user thats banned get in touch with mod team or something.