automatically affect a posting Authorizer after invoice entry/integration

Hi everyone
Is there a way to automatically affect a posting Authorizer after invoice entry/integration?
In my system lots of AP invoices have been entered through external invoices but the Authorizer Assigning Rule was not in place.
I have created and activated the Authorizer Assigning Rule. Now on newly entered AP invoices I can see that the authorizer is automatically assigned.
But what about existing AP before Authorizer Assigning Rule has been put in place? 
I have ran Update Authorization Status treatment but still no Authorizer assigned on my 1 400 invoices.
Is there a way to avoid manual add of an Authorizer?