How to correctly override table OnInsert defaults?

[nataniel]

I'm not sure if this is the right place to ask, but I'm bashing my head against the wall for the last few hours...

I am building a simple API page for Sales Header and need to be able to override the Location Code to the one provided in the request (if provided). So if I send the request like:

POST: /salesOrders
{
"sellToCustomerNo": "CustomerA",
"locationCode": "LocationB"
}

I want the Location Code on the Sales Order to be set to LocationB. Unfortunately, on the "Sales Header" table, there is a OnInsert trigger that defaults the "Location Code" (in the InitRecord() procedure)... I don't seem to be able to override this in page OnInsertRecord trigger (it's called before the table OnInsert I guess?) - so I'm stuck. I can make another request (PATCH), then it works fine, but I'd like to avoid that as much as possible.

I thought about using IntegrationEvent OnBeforeUpdateLocationCode, but I don't want to modify the standard BC behavior outside of this single API page.

Is there an answer to this? Other than "make a buffer table and insert into it, instead of directly into the Sales Header"?

[KOTRET]

What about a subscriber to the OnBeforeInsertEvent-Trigger of the Table? Could be registered manually for the session during login.