You cannot file for an extension of L1 visa, your employer can. You should have started by talking to the employer's attorney. There is a good chance you could have avoided the need for this question.
Yes, I-94 can be renewed by the employer or their attorney.
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Yes, you can extend it .. by mail to a USCIS dropbox .. not at a local office.
Talk to the company's immigration attorney, not a non-attorney in HR.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
I-94 determines your lawful presence. Your employer will seek extension if they wish you to continue to work on L-1.
This response is general in nature and cannot be construed as legal advice, given that not enough facts are known. Any comments offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship. If you would like additional information based on this response, please contact my office at 510 657 7665 or 415 902 0832 to schedule a consultation.