Rule 104.3h states:

In a multiplayer game, an effect that states that a player wins the game instead causes all of
that player’s opponents to lose the game. (This may not cause the game to end if the limited
range of influence option is being used; see rule 801.)

Is this considered a replacement effect, per 614.1a?

Relevant for multiplayer games in which Abyssal Persecutor or Platinum Angel is on the field when an instant win effect happens.

If 104.3h is a Replacement Effect, then 614.7 would kick in, but if it's a textual change to the definition of what “win the game” means, then Platinum Angel would apply differently in multiplayer.

Consider:
Player A has 500 life and Felidar Sovereign on the board. Player B controls Platinum Angel, and Players C and D have nothing relevant.

At the beginning of Player A's upkeep, Sovereign's “you win the game” trigger fires.

If 104.3h is to be read as a replacement effect, then by 614.7, the “you win the game” effect can't happen at all per Platinum Angel and the ability resolves with no effect. If 104.3h is modifying the definition of what “winning the game” means, then I should apply 104.3h first, changing Sovereign's trigger to instead say “players B, C, and D each lose the game”, then apply Platinum Angel to this modified effect, causing C and D to lose the game and the game to continue only with players A and B, since the part of the effect that says “player B loses the game” can't happen.

There doesn't appear to be any definition that I can see that states what exactly is a “replacement effect”, except that 614.1 states that replacement effects are a subset of continuous effects. It's not clear textually whether a game rule can be considered a replacement effect or if it should be invoked before considering any in-game card effects.