You are so right - I interpreted the popup-message in a bit different way, sorry for this.
So how to test Blacklisting is now working? :
a) I scanned for all operators on my SIM-card and found 26201, 26202 and 2603 (where 26202 is my default after reboot).
b) Then I set operator-selection/scan to "manual" for this SIM and just set 26201, I saw this is working fine on 26201.
c) Then I set a blacklist with just operator 26201 for this SIM and did reboot; but SIM still just uses 26201 properly and ignore the blacklisting, despite 26202 is the default-operator.
Result: Blacklisting cannot be tested since it looks like the router treats the defined 26201 as new default-operator?!?
How could I test now blacklisting is working (which did not worked in 7.02.1 when I travelled between Italy->Swiss->Germany in June).
Many thx, Rainer