Can a contractor file a lein without notice to owner or commencement filedfiled

In short, yes a contractor performing work can file a mechanic's lien. You can take steps to remove the lien from your property, and you may have a cause of action against the contractor (and that cause of action may even entitle you to recoup your attorney's fees against the contractor). 

Additionally, the fact that the contractor is alleging money due for changes to the contract is not as simple as whether the change orders were signed or not. The contractor could have defenses to the strict requirements of the contract. I would recommend speaking with an attorney to discuss your options.