Most Gloranthans believe the greater gods transcend any specific culture. Ernalda, Lodril, Magasta, Orlanth, Sedenya, and Yelm are all known by many different peoples by many different names. Orlanth is the Storm God of the Theyalans and Praxians; he is called Umatum or Rebellus Terminus by the Pelorians, Baraku by the Fonritians, Worlath by the Westerners, Wangbiao in Shiyang, and so on. A worshiper of Orlanth can travel broadly and almost always meet his god in some form; sometimes there might be different stories attached to him – the Dara Happans think Orlanth is the son of Uleria, the Ralians say he was once imprisoned by the dwarves but escaped, the Doraddi claim he killed Artmal after the Indigo Conquerer killed his son Desero.
Going a step further, many Western philosophers believe the Runes are the transcendent powers beyond culture and even gods. The Runes are “owned” by powerful magical entities worshiped by barbarians, semi-humans, and krjalki. However, these powerful magical entities are prisoners of Time, and can be manipulated and controlled by sorcerers who carefully study them and know their identity.
Understanding this was key to the God Learners’s magic. If Baraku was king of the lands north of the barrier mountains, then so must be Orlanth. And importing the cult of Orlanth to Umathela might give the Jrusteli a secure foothold in Pamaltela. If Issaries is the God of Trade, then the exporting the cult of Issaries might create neutral markets throughout the frontiers of the Empire. This cult might become associated with, add to, or even completely replace whatever god (if any) had been the patron of that activity. Thus we see Issaries cults spread as far away as Kralorela and Fonrit.
Cults also get spread by immigrants, conquerers, merchants, and foreign spouses. Nochet has a thriving Western community that reveres the Invisible God and Hrestol. The Seven Mothers first came to Tarsh with Lunar treaty wives. The cult of Sartar came to Alda-Chur along with the son of Terasarin and Sartarite cults came to the Grazelands through the Feathered Horse Queen. Ernalda came to Melib with the merchants of the Holy Country. And so on.
Thus travelers in Glorantha can find some of their own gods everywhere, albeit somewhat disguised at times and speaking in foreign tongues. However, the actual cults differ greatly in specific details from place to place regardless of what the god is called. Prayer and sacrifice, and also libation, procession, and votive gifts, are the elements of cult that make up the worship of gods in Glorantha; altar, temple, and image are the markers of space where the cult takes place. Participation in these rituals are part of what defines your identity; changing the rituals is often understood to threaten loss of identity.
Religious innovations that result in new rituals raise the specter of God Learnerism far more than learning a new story about a familiar god. Whether food intended for the gods is to be conveyed to them by burning or by having the priests eat it themselves may prove a more insurmountable obstacle than simply agreeing Umatum is another name for Orlanth.