Microsoft and Nokia have done a great job of making Lumia smartphones difficult to break into at a low-level, but software hacker Heathcliff has just proven that it's not impossible. He's just released a great-looking tool called Windows Phone Internals, and it can do everything from unlocking the bootloader to replacing the phone's ROM.
WP Internals is a completely free download, though Heathcliff welcomes donations by those who've found the tool useful. Based on the introduction video, it seems that a lot of effort went into this, and unlike most tools of this nature, detailed descriptions are found everywhere to ensure that you know exactly what's going to happen once you click a button.
According to the "Getting Started" section of the tool, supported models include Lumia 520, 521, 525, 620, 625, 720, 820, 920, 925, 928, 1020, and 1320. If your model is not on the list, don't fret: Heathcliff has said that he hopes to add more models in the future. Even if you do have an appropriate phone, you'll need to make sure that you are using one of the supported OS versions, such as the current one, 8.10.15148.160.
Even if you don't want to replace the phone's ROM or run custom software, this tool could be used to root the device and give you the ability to back up the entire thing. Options are given to back up specific partitions, or everything en masse. Later, should something go awry, you can root the device again and flash the backup onto it.
As with any kind of phone hacking like this, it's extremely important to exercise caution when thinking about using this sort of tool. Heathcliff mentions that after a tweak is done, you should unroot the device to reduce the chance of malware making its way on.
With as full-featured as this tool is, we can hope that no future Windows Phone OS update is going to kill its functionality. This could be the start to heavily modified WP OSes being released to the wild, or perhaps other OSes being flashable to the device.