So your employer is saying that they would submit a different client letter as response to to current 221g, correct?
Won't consulate see that there is a difference in location and amendment is required.
When you appear for stamping with I-129 and LCA for location A, the assumption is that you will work there. If you submit location B documents, then that assumption becomes invalid and could result in denial.
Amendment is not required to be filed while you are outside US, and could be filed after you enter US. However, you are stuck in 221g and so amendment is needed prior to entering US so that your stamping can be approved.
Did you talk to just your employer or your attorney? If the attorney has same opinion as your employer, then there is not much you can do except trust them. They are the legal experts and are expected to provide advice that results in approvals.