When viewing the details of an old AbuseLog entries, if you look at the content of wgAbuseFilterVariables in the JS console you'll notice that variables still have the old names: article_text etc. For new entries (after the introduction of new variables), new names are used. I guess this is because wgAbuseFilterVariables is generated when recording the hit, so it's obvious that it has old names. For this reason, I wouldn't advice changing them in the DB. However, we should probably map them to the new names on the fly before adding them to the page.