1. Root the x10 mini
2. Obtain the relevant build.prop file and copy to the sd card using windows or mac os x
3. install root explorer on the phone
4. open root explorer and copy the build.prop file on the sd card
5. Navigate to /system and you will see the existing build.prop file
6. Click paste and it will want to overwrite the current build.prop, click yes or overwrite
When you connect you phone to pc companion it will say that you have the latest update. ignore this and select to repair your phone. It will then download Android 2.1 and you will be ready to go!