Jagex and Old School RuneScape
See the OSRS setup hub for game context and the OSRS foot-pedal and macro-rule guide for that separate topic.
Jagex's Rules of Old School RuneScape, under “Macroing and third-party software/hardware,” says:
It means using software or hardware that can help you play the game with the software or hardware doing things for you that you should be doing yourself. Our games are meant to be played by humans …
Jagex, Rules of Old School RuneScape
This describes software or hardware doing game tasks for a player, not keyboard switch features.
If you have any doubt that something you are thinking of using could be considered breaking this rule our advice is to not use it.
Jagex, Rules of Old School RuneScape
Jagex's “Mouse Keys - Changes & Clarification” news post (January 25, 2017) is about the operating system's Mouse Keys program and remapping, not keyboards:
You may now only use your operating system's official default mouse keys program, unless it is to remap a key to any other button. If we find evidence of you using other forms of mouse keys in game, we will take action against your account.
Jagex news, “Mouse Keys - Changes & Clarification” (January 25, 2017)
Jagex, “Macro and client features not permitted” — This page covers macro and client features identified as not permitted.