Any% requires for your progress to be reset between/before attempts. This can easily be done and normal game progression can even be returned after you are done running! Here's how:
Before Attempts:
Got to: Program Files (x86)\Steam\steamapps\common\Besiege\Besiege_Data Or wherever your steam directory is.
You will see a text file named CompletedLevels. Right click it and select Copy. Now paste it somewhere safe. Now you can open the text file and you should see a set of 0s and 1s. Set them all to 0 and save it. Your progress is now reset.
Between Attempts:
For resetting between attempts, you could just open the file and type 0 for all; but it's far easier to just keep a version to hand that already has all 0s and just copy and paste it into the game files and select replace existing file.
Version 1.70 came w several changes, but the most notable is probably T-35's, Aras' Refuge, complete overhaul. Since the new version is basically a completely different level, the old runs have been moved to a different category (pre 1.7) and a new category was made for 1.7. To my knowledge, this is