Word cannot 'track' changes after they have been accepted/rejected, which is what the Changed Line can be used for. If you go to Review|Track Changes>Change Tracking Options. There you can set the colours etc. for insertions, deletions, and so on, plus whether and where to show a Changed Line. You could, for example, set deleted content to hidden (or, perhaps just accept deletions) and display additions as per the normal text in the document. That way, all that would be apparent is the Changed Lines.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]