Flash firmware without CH341A programmer In this Answer, user @y-h-wong commented that he flashed the bootrom without using a programmer. I'm guessing this was done from terminal somehow. Not sure if this is done from within OSX or from recovery terminal. Does anyone have the steps to do this?

Is the extraction process the same as if you were using the programmer?

I would like to install the full NVME bootrom drivers on my macbook air 2014 to enable hibernation properly.

A guide on MacRumors provided the step-by-step instructions to upgrade your SSD.
I guess the flashing itself should not be that much of a problem (see https://gist.github.com/elvisizer/2dfa119e959ae6f35389d4d56054f067 for further description)
The main point AFAIK is to inject a newer NVME driver into the (pre 2015) SCAP EFIPayload file that needs to be flashed.

If I understand correctly, @y-h-wong raw-edited the SCAP file (with hex editor e.g.) and copied the NVME driver from a newer Bootrom into the update for your pre 2015 MBA/MBP. The SCAP files can be extracted from the latest Mojave InstallESD (Packages/FirmwareUpdate.pkg/Scripts/Tools/EFIPayloads).

Edit:
Ok I just learnt that you can replace the NVME part using UEFI-Tool. This means, a new SCAP file can be built like that.
I'm just not yet confident enough on this to flash it using the mentioned commands, as I don't have any flashing hardware available right now and don't want to kill my system in case something goes wrong.

Edit2:
Ok, I now understand the UEFITool will only provide cap files, not scap files - meaning the file is not signed. I guess that's the reason why simple injection of the NVME section of the scap does not work like this.