The answer to all of your questions is that the company must first obtain approval not only of USCIS but also of the Department of Labor for any of these changes. In the last few months, USCIS has started making unannounced visits to H1B employers to verify employment, which includes the position, salary, location, and all the other details listed on an H1b petition.
In terms of the application forms, the company would have to file a new Labor Condition Application with the Department of Labor (ETA Form 9035) and the I-129 forms relating to the H1b visa.
Please speak with an immigration attorney about your situation to ensure that you are working within the regulations set out by the government, and to create a case strategy that works for you and your employer.
Renata Calderaro, Esq.
The Calderaro Law Group
12550 Biscayne Boulevard
Miami, Florida 33181