Ok, this is about editing the preferences file to pin package versions to something older than the most recent, if anyone cares:

1. N900's apt system ignores /etc/apt/preferences.d/* so we have to put things in /etc/apt/preferences
2. Preferences take effect as soon as you're done editing the preferences file, without needing to do "apt-get update" or anything.
3. To set the pin priority, use "Pin-Priority:" and not just "Priority:"
4. The priority should be greater than 1000 in order to force a currently-installed package to downgrade

I'm just posting it here so it will be here somewhere and Google can go index it or something. I don't mind if someone decides to move this post to somewhere more appropriate, but this is a follow-up to the last part of the first post.

If you don't understand what I'm talking about, then just ignore this post.

Btw, I tried to use numbered list bullets but it looks like this is not working.