Thanks...OK, to remove these tags do I have to do it for each album individually?
Editting the tag is relative to whatever is selected. You can select an album, multiple albums, multiple tracks. However, you have to edit the entire tag. For example, you want to edit the "Album" tag, essentially to append (e.g.) "[HD]" to the album's name, but you'd need to do this on a per album basis as there is no way to simply append "[HD]" to multiple albums.
Or, can I do a tag removal function for all albums? (I hope this is possible?)
I'm not sure what you're wanting to "remove" ... you are probably editing what is already there. You need to simply sit down with the tag editing dialog, and do it while getting used to MC's tag editing, which I'm sure you'll appreciate over iTunes' "Get Info".
[... which begs the question, didn't iTunes also group these albums into albums with "apparent" double tracks? ... i.e., both softwares pay attention to the tag metadata rather than file names or file locations ...]