First, let me say that this is not a jailbreak tool for RT 8.1! All clear? Good.
I've written a simple little driver and exe tool to patch the g_CiOptions and SeILSigningPolicy variables in ci and ntos. The obvious kicker is that you need the driver loaded for this to work -- but once loaded you can effectively use this to turn on/off the signing at will (eg: useful to avoid -- not disable -- patch guard).
I've tested this on my Surface RT as well as Windows 8 without issue.
You can find the code and binaries on github ( https://github.com/bfosterjr/ci_mod
). There isn't a whole lot of documentation (nearly zero), but you'll find batch files, windbg scripts, and various other bits which should help you figure out how it works (or you can just read the code).
Now, before you all flame me about how useless this is without a jailbreak or kernel execution for RT 8.1, let me say this: I've spent the last few days catching up on a lot of threads (over a years worth) in this form and there is enough information (if you look hard enough, open your mind, and tilt your head) in the threads to successfully start your own driver on 8.1 RT.