OEM/Original Product Code... can i use them as Alternate items?

I have product that has original code, oem codes and the original code may even change from the supplier!

eg OriginalCode - ORG1, OEM code, OEM1, OEM2

Qn1 If i use alternative items, do i have to keep an inventory of them? (OEM1, OEM2)

Qn2 Are alternative items basically product codes but just that i tag/link them to the main original code as alternate item?

Qn3 Will alternative item pop up during selection of product or its only if i am looking for alternate item?

Qn4 What about purchase of these alternative items? Will I able to input OEM1, OEM2 when I am entering the Purchase invoice?

Hope someone can understand my Qns ... thank you very much!