I'm not aware of a "standard" on this question, either now or from when I was active in the late 90s and early 2000s.

It seems like, for spheres to have any meaning at all, it has to be at the least very unusual for this to happen. I actually did it with a character of my own once, a sphere honor paladin getting tattooed by Shokai. However, that was an unusual situation where I was trying to follow a sphere with no god at the time, and Shokai's mortal background in Knights and my characters position in the Fort made him suited to the whole thing.

So, I wouldn't roll a character planning for this. But if the situation arises where it fits very well in some way I can't really imagine right now, I think it would be possible.