Thanks Helen, I've tried that three times, but restarting my phone has caused the file to remove the line I'd added. I've double checked that the file does indeed save before restarting my phone too. Is there another file/setting that you know of that I could modify to make the change persist? This is exactly the thing I've been looking for a while now so I'd love to be able to get it working. EDIT: I should probably mention I am running Lollipop, not Kitkat, which all the info I've found on this has been about.
