How to add existing taxonomy terms to node on saving I've a field organization_name which is term reference with unlimited values. Whenever somebody saves the node I want to attach a few more terms in this field.

I've tried doing using hook_presave and also using submit handler of Forms API.

But the problem is that they both expect the term to be filled with plenty other values as below. Where do I get those values? From taxonomy_term_load ?

This is the dsm out of the form_state array in the form submit handler.
The only place you need to add values in your hook_form_alter() is the $form_state['values'] array. In there you should only see the tid value, not the whole term entity.

Alternatively, you can use the Rules module