I actually don't know if it's upgraded or not. I don't see a model number anywhere on the device. There's a notice on the bottom indicating that it hasn't yet been approved by the FCC and is not available for sale. (This is different than the common models that say that it's a demo unit and not available for sale.)

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Here are the results. The backlit ROM has a different checksum than the PowerBook 100 as well as some startup code differences. Which is surprising since Apple says they are identical to the point where:

In addition, the CPU GLU Logic chip includes an ID registercontaining a unique ID that allows system software to determine that

it is running on a Macintosh PowerBook 100 and not a Macintosh

Portable. This is necessary because both the Macintosh PowerBook

100 and the Macintosh Portable have identical system ROMs.

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It is possible that your backlit contains a pre-release ROM prototype. In which case it might also be the ROM replacement on the ROM card for the backlit display upgrade and different from the 5126. That is the reason I want to see the ROM from that as well as the production backlit.

One other note of mention is that this backlit ROM is identical in the SCSI implementation with the 100, which means the Portable can do SCSI disk mode. I then found an Apple tech note confirming that a third party cable product made that possible:

https://developer.apple.com/technotes/hw/hw_540.html

Connecting two Macintosh systems via SCSI

Date Written: 12/12/90

Last reviewed: 7/26/91

However it is not clear whether it refers to all Portables or just the backlit models, but the dates seem to suggest only the backlit which shares a similar ROM to the 100.

Only analysis of the original 5120 Portable ROM will confirm this - HINT HINT