Yes, I would say they can cast it as much as they wanted. It still won’t be risk-free if they’re casting in combat — they’ll risk attracting attention, or even being killed by trying to cast right up in somebody’s face. They are just eliminating the risk of side effects. In the case of Bolt specifically, that makes it a powerful weapon, but it’s a powerful weapon that required you to take a talent to use, which sounds like a fair trade to me.
Also, the text never specifies whether Rote can be taken more than once, but if it can’t, using your one Rote to make a super weapon sounds like a fine strategy to me. (I’d even let players choose that talent multiple times, too. Up to you.)
There’s probably more than one way to answer that question, but you asked how I’d handle it, and that’s what I would do. 😄