Employee Assignment Number Best Practices

Summary

Are there best practices/recommendations for how employee Assignment Number is used?

Content

In Global Human Resources (Cloud/R12), the employee assignment number is auto-generated using C,E or N as a prefix to the employee number.  However, the assignment number can also be manually populated, as long as it is unique.  The business has expressed interest in changing the way the Assignment ID is generated; instead of being auto-generated with the letter+employee number, they are interested in using a Project/Program number.   Are there any best practices/recommendations for how assignment numbers should be utilized?  Also, is there an efficient way to identify potential impacts to changing the assignment number, since we are already live and using