Is it possible to upgrade the Laptop (1B7L1ES#ABD - 255 G7) with a second ssd or a second hdd?

[Noldi]

Is 1B7L1ES#ABD compatible with HP L20454-001 and HP L20456-001?  Other parts needed?

[Huffer]

Yes assuming you have only an M.2 SSD which, from specs, it appears you have. There is a 2.5 inch bay which can be used to add a 2.5 inch SATA HDD or SSD ultra-slim 7mm form factor. 

Service Manual 

With back cover off it looks like this inside:

M.2 SSD in red circle; HDD bay in black square

You have correctly identified the part numbers of the hard drive board as L20454-001 and the cable as L20456-001  but you also need this:

Hard drive bracket L20455-001

if you intend to install a 2.5 inch drive. There is an alternate bracket and board which can be used to add a second M.2 drive instead. The same cable is used either way. 

Found the cable on eBay:

https://www.ebay.de/itm/L20456-001-Original-HP-Flachbandkabel-FFC-zur-HDD-Platine/164236381558?hash=...

Es scheint leider etwas teuer.

Post back with any more questions and please accept as solution if this is the info you needed. 

[Noldi]

Danke für die Antwort!

Which part number for the bracket and board if I want to add a 2nd ssd?

[Huffer]

A second M.2 SSD will not be any faster than a 2.5 inch SATA SSD. The parts used for a hard drive will also work with a 2.5 inch SATA SSD. If you want a second M.2 SSD, use these:

Solid-state drive bracket L20458-001 (9) Solid-state drive connector board L20457-001

This will have to be an M.2 SATA SSD such as Samsung 860 Evo, not NVME. Again, no performance difference between 2.5 inch SATA and M.2 SATA.

Please accept as solution if this is the info you needed.