Dell Latitude 5500 series change service tag (serial number)

[techman125]

Hello.

I hope I'm in the right forum.
I have been searching for quite a while, before finding this site.
I frequently replace mainboards in the Latitude 5500, 5510 and 5520 models.
Changing the asset tag is pretty straight forward, but from what I've read changing the service tag isn't possible unless you can use a CH341A programmer and hex edit the bios.
Dell would probably be able to do it but sending them a used board and paying them defeats most of the cost savings over new.

While testing a used board and swapping parts, a 5510 just out of the blue shows "Manufacturing mode active", with a blank service tag. Don't think I touched the keyboard or did anything unusual.
So, does anyone know of a special key sequence or power on trick to duplicate this?

I used to work for an HP ASP, all it took was for them to send an MPM unlock file.
Probably just a shot in the dark, but is there any such software for Dell?
Much appreciated,
TYIA,
brent

[techman125]

5/19: Update - Dell Tech Support says there is no procedure to change the Service Tag. A call to an authorized Dell Warranty provider says they have no way either. Though I was talking to customer service, she did say that she asked the Service Dept., so who knows.
So, still stuck on the option of Manufacturing Mode.
Any retired Dell service techs here that can at least comment??
TYIA