3 months ago, I changed the theme of my website to Mystique theme, which is great !

However, I have a little problem with the layout of older articles.

Since the installation of Mystique theme, I modified a litter bit the layout of the page (insert some widgets, etc). For older articles (which were posted from another theme), I am not able to change the layout:
Here is an example of the current layout: http://macrecord.com/2012/02/01/os-x-lion-10-7-3-disponible-au-telechargement/
and an old layout: http://macrecord.com/2011/10/13/foule-impressionante-a-lapple-store-opera-pour-le-lancement-de-l-iphone-4s/

Is there a way to automatically change all these old articles to the new layout?

Thank you!