with my internet provider I use 2 email addresses: name@pandora.be (original address) alias name name@telenet.be (new address)
in my windows live mail imap account there is (and always was) name@pandora.be configured
can I change the properties of my account to email address name@telenet.be without any problem?
I don't touch username and password
Yes, you can change the From: address, but it's possible that will cause a sending problem for you if you send out the original sending servers and they don't allow it and/or the SPF for telnet.be doesn't allow it. It should be safe to try it and see if it works. If not, you can always switch back the settings.