As the title

Can I make art assets, and create some general code template (like a 2D controller, just for example), before the Jam starts?

I can't reply with the intended answer by the Host, but i'll share my opinion. 

Making asset before the jam start falls under premade assets which are allowed... Also, template sounds great as long as you don't work on the jam game before the jam start. 

I might be wrong about this.