READ the below site it says "The Service should continue to expect the applicant to submit a letter notifying INS of this
change in intent" reach you your own conclusion:
http://www.immigration.gov/graphics/lawsregs/handbook/ac21guide.pdf
1. Procedures for Processing Benefits under AC21 106(c)
F. AC21 106(c) - Change of Employment Permitted in Cases of Lengthy Adjustment
Adjudication
The AC21 106(c) provides that the certification or Form I-140 approval of an EB immigrant
petition shall remain valid when an alien changes jobs, if:
(a) a Form I485, Application to Adjust Status, on the basis of the EB immigrant petition has
been filed and remained unadjudicated for 180 days or more; and
(b) the new job is in the same or similar occupational classification as the job for which the
certification or approval was initially made.
1. Procedures for Processing Benefits under AC21 106(c)
If an alien has complied with the above statutory requirements, adjudicators shall not
deny applications for adjustment of status on the basis that the alien has changed jobs. Under
present practices it is expected that an I-485 applicant notify the Service when they no longer
intend to enter into employment with the employer who sponsored them on the I-140 petition.
The Service should continue to expect the applicant to submit a letter notifying INS of this
change in intent, if the Adjudicator has reason to believe that the applicant's intent has changed a
Request for Evidence (RFE) may be issued to clarify the applicant's intent in regards to
employment.
In instances where the applicant no longer intends to be employed by the employer who
sponsored him/her on the I-140, the Service should request a letter of employment from the new
employer. The letter from the new employer verifying that the job offer exists should contain the
new job title, job description and salary. This information is necessary to determine whether the
new job is in the same or similar occupation and to determine whether the alien is admissible
under the public charge ground of inadmissibility at INA 8212(a)(4). To determine whether a
new job is in the same or similar occupational classification as the original job for which the
certification or approval was initially made, the adjudicating officer may consult the Department
of Labor's Dictionary of Occupational Titles or its online O'NET classification system or similar
publications.
The Service is currently formulating proposed regulations to establish a policy
framework in which to adjudicate AC21 106(c) benefits. Until the Service promulgates final
regulations establishing such a policy framework, adjudicators shall consult, on a case by case
basis, with Headquarters before denying cases on the basis that the new job is not in the same or
similar classification.
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According to my opinion if you send a letter of Intent change it will not hurt but they may not read it or attach with your file but nothing wrong in sending a letter they only EXPECT and it is not MUST. You may have to send the letter again if they send you RFE before final stage.