Can a blocked contact see any number changes? I would like to ask, whether a blocked contact will receive an information,if I change my Viber phone number? 
Is it possible to make the change by only informing a selected group of contacts or everyone I had previous communication with, will get the notification of me changing the number?

Thanks
They will not notice it unless they try to make contact with you after it is done. But things can become awkward if you are both a part of the same group chat. You won’t see their messages but they will see yours. And as a rule, if they are blocked, they won't see any changes of yours.