If you mean by your question you want to change just the wall socket to RJ45 and still use it for Masterlink, then your first problem will be the number of connections. Masterlink requires 9 wires plus ground connection.
If you mean you want to use the Masterlink cable for the transmission of Ethernet signals instead of Masterlink, then you are likely to have a few issues. The core reason is that for the higher digital transmission speeds of ethernet. The Cat 5,6,7 cables consists of twisted pairs and shielding which cancels out most pickup noise, the Masterlink cable shields the analogue signal and control and has a differential signal, but cannot deal with the higher speeds particularly along a longer piece of cable without problems. Also, because of the structure of the Masterlink cable at least one pair of ethernet signals would have to travel down non shielded and non twisted wire.