I'm not quite sure what you are trying to do, or why you are trying to do it this way, but if you need an svalue that can be modified later, you can use for example a mapping. Anyone who has a reference to the mapping will be able to see changes you make to it with the []= operator and things like m_delete().
Strings, on the other hand, are immutable, so you can not change the value of a string value you have already passed to someone.
