If they think it'd be a fun experience or if the power set just isn't working for them, players can switch their character's main power type at anytime. Players just have to contact the mods and let them know. So your character can potentially switch from "Roughing It" to bonding with a "magic weapon" in the setting, as long you contact the mods when you want it to happen and request it.

As for other people's magic weapons, they can summon the weapon to them under most circumstances, and any magical abilities will only work with the owner they're bonded to. So if Cassie were to pick up another character's magic weapon it'd only work as a normal weapon for her and the owner could recover it at any time. Magic weapons that are ownerless will also be rare in the setting, so finding and bonding with one randomly in the setting would have to be worked into a plot. (The mods would be happy to help you with this when you want the switch to happen).