Convert between FileVault 2 and Disk Utility encryption?
As it turns out, I found the answers to most of this not long after I asked the question.  The command-line fdesetup program offers some additional options.

Removing Disk Password

Run sudo fdesetup list -extended and look for the UUID labeled "Disk Passphrase".  Then run sudo fdesetup remove -uuid &lt;UUID&gt; to remove it.

This can be used to remove the disk password that was created via Disk Utility, leaving only user login passwords for unlocking the disk.

Removing User from FileVault

Run sudo fdesetup list (-extended isn't needed) to see what users are authorized to unlock the disk, then use sudo fdesetup remove -user &lt;USER&gt; or sudo fdesetup remove -uuid &lt;UUID&gt;.

This can be used to de-authorize users so that only the disk password can be used.

Adding Recovery Key

Run sudo fdesetup changerecovery -personal.  This will prompt for a password (anything that's currently enabled to unlock the disk), then display the new recovery key.  (Write it down!)

Removing Recovery Key

Run sudo fdesetup removerecovery -personal.  As above, this will prompt for a password.

Adding Disk Password

I couldn't find a way to do this in-place — sudo diskutil cs passwd seems like it ought to work, but it requires there to be an "old" disk password already.

However, you can turn off FileVault using the preferences window (which decrypts the disk), then use sudo diskutil cs encryptLV &lt;UUID&gt; to re-encrypt it with a disk password.  This is slow, since it has to decrypt and re-encrypt all the data, but it works.