Has any purpose been discovered for the HR swordsmith guild, that is present for Toledo and Damascus? Is it safe to use the HR for other purposes or to replace it?
Generally the swordsmith guild is easy to get in campaign for most factions that can train sword infantry.
In vanilla the Moors have two sword units that will get the swordsmiths guild - Urban Militia in cities and Dismounted Christian Guard in castles in the late game. Otherwise the Turks and Egyptians have no sword units. Ditto for the Russians, who can't get it. If descr_guilds is amended to the conditions "type infantry/class heavy" (as in KGCM) the Egyptians (halberd militia) and Turks (halberd militia and Janissary Heavy inf) will only be able to get the swordsmiths guild in cities. They don't produce any heavy infantry in castles.
That said, the Russians, Egyptians and Turks don't greatly benefit from a swordsmiths guild. Their strength is in their archers and horse archers. Generally they gain a swordsmiths guild through acquiring those of other factions.