As far as I know, this should not be a problem as both share the LGA 1151 socket and the same 14nm lithography. However, a BIOS update will be necessary to maintain good stability.
As an example, this would be 2 x 16 GB 2.133 MHz: https://www.digitec.ch/de/s1/producttype/arbeitsspeicher-2?opt=v10-7967:2|v10-7804:160000000&pdo=10-3195:8135|10-420:185139&tagIds=76
I have the device on the beamer in the living room for the HTC Vive and as a media centre with Plex. The device runs perfectly and is compatible with the codecs that my AV receiver supports (although this is largely dependent on the software). The heat and noise development is at a low level. So far, everything fits. Depending on the intended use, however, the device is certainly too expensive and overdimensioned.
From their website (https://www.asus.com/ch-fr/ROG-Republic-Of-Gamers/ROG-G20CB/) it looks like it is ddr4 and a m.2 SSD (not said in description either).
If you are willing to put this amount of money in a desktop computer I can only advise you to build one yourself. With this one I don't know if the possibilities of upgrade are great because of the space. If you have any question do not hesitate.
I recently spoke to a repair service provider (warranty case) about a notebook on which I had exchanged the SSD. The statement was: According to Swiss law, a device is your property after purchase and you may convert/upgrade it as you wish. As long as the reported defect in a warranty case cannot be linked to the conversion, the warranty is still guaranteed.