This wont work unless all your code is in main:: (and even then its a delicate situation at best)

#!/usr/bin/perl

sub main::croak {
    print "I croaked";
}

{
    package Test;

    use Carp;

    sub myfunc {
        croak("I am dying");
    }
}

eval {
    Test::myfunc();
};
print $@ if $@;


*myfunc = \&Test::myfunc;

eval {
    myfunc();
};
print $@ if $@;

__OUTPUT__
I am dying at test.pl line 18
I am dying at test.pl line 26
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