Thanks for checking back in, @WB19. 

I hope you're having a great day so far. 

If the account you're referring to has any transactions associated with it, then yes, it will affect any transactions connected to it. As my colleague has mentioned above, if you change the COGS account number for parts you sell the account number change will apply retroactively and affect historical transactions using that account.

For more information about closed books, check out: Close your books in QuickBooks Desktop. 

Please don't hesitate to let me know if you have any additional questions or concerns. Take care!