Currently Being ModeratedDec 12, 2012 3:59 PM (in response to Rob Marquardt)
If I understand you correctly, you have music that is already in iTunes Match and "in the cloud", and now you're replacing the files? To do that properly, you need to first delete the song from the cloud because Match will only try to match/upload new songs (not replacement files).
On the 3rd Mac - the one with no music - delete the songs that you are trying to update. That will remove the mp3 version from the cloud. It does not affect the Mac with the local files (the warning is a little confusing).
Then go back to the Mac where you ripped the CDs, right-click the songs you are updating, and choose "add to iCloud" - that will cause Match to re-add those songs. You might have to update Match first, so this Mac realizes that the old files are gone from the cloud (that will happen automatically, but you can make it happen now in the "Store" menu).
Currently Being ModeratedDec 12, 2012 4:10 PM (in response to Joseph Delaney)
That did the trick — thanks! It even retained ratings and play counts!
When I delete the cloud version from the third Mac, the iCloud status of the track on the ripping Mac changes to “removed” almost instantly.