OK Command Button

Hello, good day, I ask for your support to know if it is possible to perform the following scenario.

It is desired to modify the normal behavior of the Quote/RFQ when the quotation comes from a Purchase Request (PR), and one of the elements split into 2 or more suppliers, it only allows it to be done with a single supplier, modifying the PR to later create the PO; it is desired that although the RFQ is linked to a PR, it generates the Purchase Orders of the article that has several suppliers (when it is a direct quote it allows to split a line with different suppliers and generate the n' POs for each of the Suppliers).

My doubts / questions are as follows

1-. How you can track the classes / methods that launches the OK Command button of a form (PurchRFQEditLine)?.

2-. Will Microsoft allow me to modify core classes that affect the OK Command Button?