Changing job should be safe after 6-months.
Changing job should be safe after 6-months, especially for NIW. If you are called for an interview or you are issued a RFE for job(that may happen if your I-485 has not been approved after long time), it would be better if your new job is similar to your old job which was described in your 140. If no interview, no RFE, no need to consider job difference.
BTW, I sent you a private message about finger prints. Could you please check it.
Thanks.