Welcome 'paulindr'.
At first we have to make sure that you speak about the tagger application Mp3tag, current version 2.58. You are on version 2.55? Why not update?
Mp3tag allows to open one folder only or a folder tree, this behaviour can be set by checkbox in Mp3tag options. Try it out.
You can hide or select files from the current listview by invoking the Mp3tag Filter [F3] dialog and by applying an appropriate filter expression.
See manual for details and examples ...
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DD.20140313.0932.CET