Yes, you can use an unlicensed version of Darkroom Booth to design templates. This is handy if you typically use a computer other than your photo booth computer to design graphics. Most photo booth operators have computers dedicated or installed in their photo booths with their licensed version of Darkroom Booth. And then use another computer for graphic design. Install and use Darkroom Booth software on any computer in trial mode to create templates in tandem with Photoshop or whatever image editing program you prefer. Transfer finished templates to your photo booth computer in any number of ways including email, an online cloud service like dropbox or a good old fashion jump drive.
Below is a video tutorial with more details.