You're talking about the functions of the OS characters in the Overall Story, right?
If so, there's almost total flexibility. The only hard rule is to avoid putting a dynamic pair of elements on the same player, e.g. don't have one character represent both Pursuit and Avoid.
Ok, one other hard rule - don't double dip on elements, i.e. don't have two characters play tug-o-war with one element (but you can have multiple players collectively embody an element, like how Fischer's army of mind-guards all play the antagonist in Inception)
The themes, issues, and elements of the OS Throughline as presented in the PSR are a different beast, they are faced by all the characters in the Overall Story as a group. One common perspective. But OS functions (ala the archetypes) you can divvy up and parse out pretty much as you please.