I like to change the theme in my E71 frequently, I get easily bored with them! To solve my little problem I installed a really cool app that changes your theme on a preset time or when the profile is changed. With this app you can program your E71 to change theme every hour or even every 5 minutes!
I personally use it to make my E71 go according to the day and night, I have two themes, one light colored theme and other with dark colors, the white theme is automatically activated during the day and the dark theme is automatically activated during the night and the next morning the white theme comes again when the sun is rising. This is just how I use it, there are many other ways to use it, have you tried it?
To try it download it here: http://drjukka.com/ThemeScheduler.html
After having the file downloaded to your computer follow this tutorial to sign the application.