"Client-Change while I 129 pending"

My Employer had filled my H1 B petition last month and is under initial review. I am on CAP GAP Ext. Currently I am working for a Contractor (My Employer) --> Vendor A–> End Client A. I have filled my H1 petition and shown my Client as A and provided client letter and PO while filing my case.

But now I have got a job offer with another client same job profile and field however so there will be change in the end client. So, if I go through the Same Contractor (My Employer) --> Vendor B --> End Client B. So, my concern is can I go through this as I am just changing my Client as employer would be same. 
What could be the implications with change of end client? 
Can amendment in H1 petition be helpful in my case? 

Thanks in advance for reply.