I haven't been able to find a solution for PowerShell yet, but you should be able to rename the files via command prompt using something like this:
ren \\.\<absolute path> <new name>
So for example:
ren \\.\C:\stuff\con.cfg stuff.cfg
You could invoke the command prompt through PowerShell, of course:
cmd /c "ren \\.\C:\stuff\con.cfg stuff.cfg"
And obviously you could use PowerShell variables in there if you wanted
$dir = "C:\stuff"
cmd /c "ren \\.\$dir\con.cfg stuff.cfg"