In the post where I set out my intentions for
Bulk change from common to rare, I proposed to make both
metered and
mitred rare.
Reading Gaye Christine's comment, I think
metered should remain common. The spelling
meter is used in both America and Britain for a measuring device, and the word
metered is in quite common use, especially in "metered parking", but also for metered water, etc. The
metre spelling is not used in the US, but even in Britain and other places where it is used for the metric unit of length and in connection with poetry, the word
metred is very rarely used. (I found no example in the British National Corpus.)
As for
mitred and
mitered, they do have the same meaning, one in the US and one in Britain, so they should be treated the same way. This is not the rarest of words, and many people would be familiar with it as describing a type of joint in woodworking. But probably many others would
not know the word, and when in doubt I usually go for rare, so I have made
mitred rare to bring it into line with
mitered.