In short, it seems that the poster had inflated the CTC offered by Company B on his own. It also seems that the poster himself has realized now that what he had done is not ethical, and that guilty feeling alerts him to whether his act would come to light if a BGV is done by Company A.
Certainly, it is possible if the scope of the BGV includes not only the verification of previous employment but also the previous offers the candidate mentioned. Particularly, since the poster has mentioned that he himself edited the offer of the sum of "y" by Company B as 'y+' in order to get a higher package from Company A. It is nothing but tampering with records for the sake of personal gain, and as such, it would clearly prove that he is not a reliable person.
If the BGV process is restricted to previous employment only, of course, it may not come to light.
However, the poster should bear in mind that honesty is the best policy for every job aspirant. He could have negotiated for a higher package since the same was also offered by another company, which he didn't accept.