try it. you won't be dissapointed. many ways to customize. even in a less official way.
I mean for example if you don't like 100% of a skin, you can modify them by opening the package contents (contents>resources>scripts>skins), everything should work ok as long as the setting.xml file and the smileys folder keeps together.
e.g. I want one that look like MSN 4, but the MSN4 smileys are all static. not animated. what I did is taking the setting.xml + smileys folder from the MSN (yes, just "MSN") folder and put it in the MSN4 one. oh, animated smileys now!
also if you want to put your own way of writing as language, check out contents>recources>scripts>lang and modify the phrases in one of the language (langen = english).
idem for the app's icon (contents>recources>Wish.icns), the user pics, the used images for the UI, the sounds, etc... but maybe make a backup before ;-)