Don't return your

string representing what went wrong.

Code that reports an error should die.

This is called throwing an exception.

sub methodfunction {
    # take a spoonful
    die 'too hot'  if $temp > $hottest_allowed;
    die 'too cold' if $temp < $coldest_allowed;
}
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You ask:

in my script that calls the method, can I save the returned string somehow without saving it directly to a $variable?

Yes, if your script wraps error-prone statements in an eval block, it can find the error in $@ (or $EVAL_ERROR if you use English). Admittedly this is a variable, but at least you didn't have to declare it.

sub rollback {
    my $undesired = shift;
    print "That was $undesired. I shall try another bowl.\n";
}
# and later ...
eval {methodfunction()};
rollback($EVAL_ERROR) if $EVAL_ERROR;
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The advantage of working in this way is that everyone who reads your code will understand that the string in question is an error string. It's confusing to have the only return value of a function be an error.

    { rollback( methodfunction() || last ) }
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    my $variable = methodfunction();
    rollback($variable) if defined $variable;
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I'd say just put this at the top of rollback():

return if ! defined $_[0];
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I don't recommend this, but it almost works:

rollback( methodfunction( 'foo' ) or goto NO_ROLLBACK );
NO_ROLLBACK:
print "done\n";

sub rollback {
    my $s = shift;
    print "rollback('$s') called\n";
}

sub methodfunction {
    return $_[0];
}
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Try it with undef instead of 'foo', and you can see it skips the call to rollback. However, it also does this for other false values (0, '0', or the empty string).

Maybe an other approach is interesting for you too. See Best Practices for Exception Handling

You could use the default variable:

rollback($_) if defined ($_ = methodfunction());
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rollback (methodfunction ())
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sub rollback {
    my $reason = shift // return;
    ...
}
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