Substitution of Labor Certification of a laid off employee

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Hi All,

I need some advice on substituion of Labor Certification: Company 'A' filed and obtained a Labor Certification for Mr.'X', then due to layoffs in the company, Mr.'X' was laid off. Now, Is it possible to use Mr. 'X's labor Certification for Mr. 'Y'?? and file I-140 without filing Labor Certification for Mr.'Y'. Will it lead to any problems during I-140 process and its subsequent stages (say CP). In the meanwhile, the Company has also filed a Labor Certification Application for Mr.'Y'. Since the processing times are so huge, is it possible for Mr.Y to use Mr.X's LC.
If so, What will happen to the LC filed by Mr.Y. Can it (application) be taken back.

Thanks in advance