NativeMultiHashMap updates

I'm using a NativeMultiHashMap for Spatial Hashing. When I move objects, I need to update the map - which involves reading the existing values via a NativeMultiHashMapIterator, removing the value using that iterator and then adding the value again against a new hash value key.

I'm just wondering about how to schedule this efficiently. Only the additions can be done concurrently using NativeMultiHashMap.concurrent, so presumably I need a job for reads/removals followed by a parallel job for additions? How would that look? Do I have two jobs in a System (or can a system only have one job?) or should this be multiple systems? Sorry - this is probably basic stuff but I can't figure out how this should look.

Thanks for any help!