Changing a player's projection changes how that player performs in the simulations, which changes how often they show up in your lineups the next time you build.
Nudging a player up makes their game scripts a little better, so more lineups get built around them. Nudging down does the reverse.
Changing a team total shifts the whole game script and lets the simulations decide which players benefit, which is often the better move when your read is about a game rather than one player.
The change doesn't touch lineups you already built. Rebuild to see it.
Move in small steps. Adjust 5% at a time and rebuild, because small changes have a bigger effect on lineups than they look. If what you actually want is a specific amount of a player, set an exposure instead. Projections shape the game story, exposures set the portfolio directly.