In this case the "Mass Transfer" action being performed is clicking the Change Owner link on the parent Account record which subsequently bulk-reassigns the child Opportunity owners and does not execute the Opportunity [before | after] Update triggers nor does it execute a Workflow action on Opportunity.
I attempted to add a workflow rule to opportunity that runs on create and edit and increments a field, but alas it doesn't run during this particular operation.
How (else) can I cause these Update triggers to execute during this type of operation?
Opportunity triggers are not fired when the account owner changes as a result of the associated opportunity's owner changing.
When you modify an opportunity product on an opportunity, or when an opportunity product schedule changes an opportunity product, even if the opportunity product changes the opportunity, the before and after triggers and the validation rules don't fire for the opportunity. However, roll-up summary fields do get updated, and workflow rules associated with the opportunity do run.
(Note: I am not modifying an Opportunity Product nor Schedule but would love for the workflow rules associated with the Opportunity to run...)