Just updated the beta branch again today, adding special seed codes. Use these codes for special alterations in how your level is constructed:
777777 - Flat lands
101010 - Lots of jumps (pits, etc)
123456 - All uphill
654321 - All downhill
111000 - Level length reduced by 50%
They also work in Multiplayer.
Update log:
http://steamcommunity.com/app/248330/discussions/0/451850213946308525/