Can the link disavow tool be used more than once? Yes, use it more than once. However, disavow a different collection of URLs each time. Do not disavow the same URL more than once.
The bigger question is whether or not to use it at all. Some may be concerned that Google is using this tool to trap link spammers. After all, Google is not clear on this. Though it is not likely the intent of the tool. Knowing Google, they do not need this tool to point out junky links. They likely already know about it.
How to use it? As Matt Cutt’s says, use it like a Machete. Use it to cut entire domains. Do not use it for each individual link on the domain.
