Can I add javascript dynamically to an existing script element

I want to dynamically add javascript to an existing script element something like:

var se = document.createElement('script');
se.setAttribute('type', 'text/javascript');
se.innerHTML = 'alert(1)';
document.getElementsByTagName('head').item(0).appendChild(se);

The interesting part is se.innerHTML = 'alert(1)'; and if it is valid? If not how can I do this the right way?