That’s a very good question. I used to do the same with DevianArt stock. Some were allowed for reuse, others less so. As long as you are strictly just trying stuff out on your computer, it’s all good, nobody can sue you for that. The moment that becomes a published item though, even if you offer it for free, you’re in trouble, so make sure you get every signature necessary before any of it ends up anywhere else but your computer.