how to change other smtp address?

Exchange 2010 sp3, Win2k8 R2 AD

my proxyAddresses contain several email address:

SIP:12345@acme.com
SMTP:Bbunny@acme.com
smtp:Bugs@somedomain.com

i can change the primary SMTP address because there's a switch for it (-PrimarySmtpAddress) like this:

$Users = Import-CSV c:\myfile.csv
ForEach($User in $Users)
{
set-mailbox -identity  $user.loginid -PrimarySmtpAddress $user.primaryemail -EmailAddressPolicyEnabled $false
}

but how to change the second smtp address (smtp:Bugs@somedomain.com)?