Both Merged Result and Original Merge Request Pipelines

I have read the documentation that I can find on “Merged Result” MR pipelines, and I cannot determine the answer to this question:

Is there any way to have automated CI checks/jobs run against both the Merged Result commit and the original commit that was pushed.

I understand how to use rules: -if: $CI_MERGE_REQUEST_EVENT_TYPE == 'merged_result' to condition a given task on whether or not the pipeline is a merged_result pipeline, or a “normal” detached pipeline. … But AFAICT, when I enabled merged_result pipelines in the project settings it turned all the pipelines into Merged Result pipelines … and the original pipelines on the original commit just don’t run at all?

To put it another way, enabled Merged Results pipelines in settings seems to have turned:
rules: -if: $CI_MERGE_REQUEST_EVENT_TYPE == 'detached'
into
rules: -if: False