Overwrite or change doc_event from ERPNext

first of all… i know to not change erpnext python code because of overwriting after update to a newer version…

but… i need to overwrite an existing hook with my code and code from erpnext should be ignored… and i need some extra hook for a doctype at the beginning of all hooks ( or after all other hooks has been runing )

now… i know where the code is in erpnext directory but how can i change functionality to my explaned cases ?

your real use case?

yea… i would try…

Case 1… adding hocks to doctype item ( for extra functionality )
Case 2… adding calculated values with befor save for validation ( salesorder as example )
Case 3… mark items as deleted and disable all hooks on this particular item ( for example salesorder )

maybe this is a problem because of does not knowing what runns in the original hooks … but i need to do some extra functionality and does not want to break things from the default erpnext app