Depending on the extent to which we consider something "Satanism", I could see a sort of pro-satan "simonianism".
The quotation marks are important here as I think it's worth distinguishing this hypothetical Simon Magus based belief system from the later movement which bore his name (but held dubious historic link to the actual figure). Otl simonianism was a gnostic movement that was heavily Christianised in it's nature.
Rather, I would suggest for this challenge looking at commonalities of accounts of Simon Magus, which hold him as a magician and someone who also claimed to be the Messiah. He typically converts to Christianity and is either admonished or does horribly (but we are going to look past that for now).
This, is where Satan comes in.
Presuming Simon liked to demonstrate their "power" or was at least believed to have done so, then the temptations of Christ in the desert take a very different tone. Prior to this, Satan has been God's advocate and tester, challenges Jesus and Jesus doesn't take him up on those challenges.
Our "simonianism" rather points to this as Jesus having failed to live up to the title of Messiah and instead posits a story where Simon does indeed do the things challenged of him.
Fundamentally, this does 2 separate things. The first is that it creates a natural opposition both culturally (a religion born of Jews Vs a religion born of Samaritans) and theologically (different Messiah and attitudes to the nature of the messianic) whilst putting Satan as the epitome of this divide.
For the Christians, Satan has to be the deceiver or their Jesus is illegitimate.
For the Simonians, Satan effectively acknowledges and crowns Simon on god's behalf.
Ultimately, both religions would probably be fairly similar to eachother, but we would have one faith that outright praises Satan and fairly well meets the OP challenge.
At this point, you just need some reason for the 2 to survive independently.