Collectors, Collector Groups and Employee Resources assigned to a Customer

We are using Advanced Collections and are considering using Collector Groups assigned to Collectors in order to assign work to different Employee Resources.
I found a note that says that work is assigned randomly to Employee Resources from the pool of Employee Resources attached to the Collector Group.

When a work item is assigned to an Employee Resource for a Customer, will the system always assign work items for that Customer to that same
Employee Resource?

In what circumstances might the Employee Resource be changed for that Customer? We would prefer for the Employee Resource to remain
consistent for the Customer unless the Employee Resource is specifically changed.