Registry Editor allows you to apply tweaks and gives you full access to the registry. However, you will first need to unlock your windows phone
Registry Editor for WP7 is a nice and full-featured registry editor and works on all WP7 devices, you can explore and search registry, create/edit/delete registry keys and values. Registry Editor is for advanced users only, be careful using it, you have a full access to the registry, so deleting or modifying some values may result in unstable or unusable system.
Note that it is only said to be fully working on only HTC windows phones. If you own a Samsung WP7 phone, check this registry editor for samsung wp7 devices.
download from here