Quick question about valid username characters

[Michael Kearey]

Hi There,

I have several multi-user machines running Redhat 8.0. There are 
hundreds of usernames on these machines that have mixture of upper and 
lowercase.

I may be able to just upgrade, but I would prefer to install new 
Fedora, and automate adding the existing users on old Redhat 8.0 
machines to new Fedora ones.. (Several reasons for doing this, but not 
relevent here)

I have since discovered that Fedora (And Redhat of course) at some 
stage changed , or maybe more properly, now enforces usernames to 
allow only lowercase.

I'd like to know precise details :

Why the change?

Any simple way to circumvent the 'feature' (I know vipw allows you to 
do it, but I need an automated way !!)

Is there a changelog anywhere in appropriate rpms that explain the change?

Any other advice and info would be much appreciated.

Cheers,
Michael