If you can write conventional then all you need to do is add a new trunking system then delete the old one. You will have to do same for personality.
+1 on this, there has to be a trunking system, but if the only one requires a system key, then another must be made first, then delete the one with the system key, in that order.
Happens all the time where I work, we have interoperability with fire stations nationwide, and retool radios from different cities and regions, they often have system keys for parts of the country we do not have physical access to the keys.
Also fun when they come back for repair and have to go to various entities to have Zones added, with different keys per zone......you find who knows what they are doing, the weak end up deleting everything but their "System"/Zone.