use myPackage;
myPackage::foo();
myPackage::bar();

##</code><code>##

package myPackage;

use strict;
use myNewPackage;

# magically convert myNewPackage::* to myPackage()::*
# except for one function where myNewPackage::bar() needs to actually provide myPackage::old_bas()

##</code><code>##

sub myPackage::a {
    return myNewPackage::a(@_);
}

sub myPackage::b {
    return myNewPackage::b(@_);
}

sub myPackage::old_bas {
    return myNewPackage::bar(@_);
}