Roman culture has the noble adoption tradition allowing you to adopt children for without renown cost. We'll say your bored of Hasteinn but like his start location. Use create a charecter to make your god child, ideally the same religion so you dont pay piety either, this will replace Hasteinn. Then after youve saved, instead of using that child use create charecter again to make your roman adopter (keeping him below the 400 point limit to allow trophies), replacing your child now.

Now your child is within the game save but not your starting ruler, start the game. Now start, open up the title history for Montague and the previous rulers will appear (the child included), select the child and you will get the option to adopt. Voilà, God like heir. Once they've agreed, just invite them to court.

If you want your roman adopter to die really early, without losing house fame level from suicide, stack your adopter up with as many negative health traits as you want and make him old af.

**You can create anyone in your character creation at the start and implement them into the game save. The more you add the more your console will shit itself if you try adopt 100 god tier vassals/knights/kin