Yep!
Instructions for level creation:
Any resolution PNG should work, but try keep it small, the default ones are 10x10 to 21x21. Doesn't have to be square.
White (255,255,255) is empty space
Black (0,0,0) is for walls
Blue (0,0,255) is the player spawn. Please only place one
Green (0,255,0) is the exit, please only place one
Magenta (255,0,255) is briefcases, please place at least one
As for the guards they are a little more tricky:
Every patrol has the colour (255, id, order) and the guard will spawn on the lower order. Order doesn't need to be consecutive.
So for guards you can do (255,0,0) and (255,0,20) to set up a simple two waypoint patrol with one guard.
To add another guard you could use pixels with (255, 5,0) and (255,5, 7).
Lastly, levels are loaded alphabetically, so if you want to test your own level quickly, either remove other levels or rename yours to something that will come before "01-intro"
If you need any help just ping meon here or on twitter, I'd also love to see what you make!