Maybe something like this  (it doesn't exactly rename the package, but rather just copies its symbol table hash):

#!/usr/bin/perl

package Foo;
sub bar { print "bar() called.\n" }

package main;

BEGIN { %{*NewFoo::} = %{*Foo::} }

NewFoo::bar();  # calls Foo::bar();
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or without BEGIN, in which case you need to postpone the compilation of NewFoo::bar() until runtime using eval:

...

%{*NewFoo::} = %{*Foo::};

eval q|NewFoo::bar()|;  # calls Foo::bar();
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