- Have a non-scenic route for the ride south already plotted and saved, for when you're out of time / riding at night.
I know it's within the rules but is it common practice to make your own route between controls even if that results in an easier and/or faster time?
It more-or-less depends upon the rider. All you need do is look at a map - the official route is one that will work for anyone, anytime, as it avoids shit A-roads, dodgy crossings, rough lanes and all the other fun of riding in the UK (where possible). But we're all adults as riders, and we can make our own decisions on routes.
Some people will be happy to follow the route - and TBH, it'll be a more social ride, as you won't get to chat with other riders much if you flog along the A10, A19 or whatever - but the alternatives are available to anyone.