I am about to "release" my own set of actions that deal with Mixed Case in what I called "Enhanced" way, because it deals with many exceptions and particular situations, in which you forcibly want upper-case (e.g. OST, P.S.) or in which you want lower-case (e.g. of, a, the, an, in, etc.)
So I created three actions.
1.1. Mixed Case ALL (Roman Numerals, OST, Publishers, MediaTypes)
1.2. Lower Case ALBUM (A, THE, OF, AND, AT, IN, AN) (ENG, FR, PT)
1.2. Lower Case TITLE (A, THE, OF, AND, AT, IN, AN) (ENG, FR, PT)
The first MixedCase simply puts everything in all fields in MixedCase.
It also works with Romans numbers, up to 50 (L). I think no one will need more than that, and the greater the number of characters used, the greater is the risk of messing things up.
Pay attention to URLS in comments and other fields, because it also does it in them, and might break some links that are case sensitive (anything after the domain name).
But that is the only problem I know of and I already tested in several hundreds of files in three different languages.
The other two are to be applied optionally if you want lower-case articles (a, the, in, of, etc.).
They only affect the mentioned fields ALBUM and TITLE. I did them separate to provide more flexibility, so that you may do one without the other.
They work for articles in three languages already: English, French and Portuguese.
It is still under development (but you may help too if you want), but I think most cases are already being taken care of.
Try it with a few of your tags just to see the effect and check if you like it not.
This is only a "beta" version, so I'll will wait a few more weeks to release a final version in it's own thread. But since you are already in need, here it is.
Hope this may help.
The file I attached is in Zip format and contains the 3 actions. You just have to extract and put them in the correct mp3tag folder: [...]\Mp3tag\data\actions
Mp3Tag_Actions_EnhancedMixedCase_Conversion_Nature__2014_06_24_.zip (1.76 KB)