A
The 40 players on a team's "40-man Roster" are the only players who can participate in an official MLB sanctioned game, including Spring Training. Team have what you call "NON-ROSTER INVITES", but this game DOES NOT, and have never had that feature.
To play with another player who is not on the 40-man, you must remove someone from it, and add that player to it.
I’ve been a baseball fan since I could remember (37 years old). It was the first sport I played as a kid that I was actually good at (played baseball before soccer, go-figure right) and it’s always stuck with me. I love the sport. It’s my favorite sport, far beyond my number two sport of soccer. I’ve played EVERY baseball game you can think of. All-Star Baseball on PS and N64, Ken Griffey Jr’s Winning Run, MVP Baseball. MLB 2K. You name it. I’ve played it. True franchise player and love it. MVP Baseball was my jam, but once MLB 2k took over, I lost interest in the game (2K is the reason I stopped playing football and basketball games). When the show dropped, I was all in, and have been playing MLB The Show since the beginning. I know they’re not showing franchise as much love, but we’ll get there (M2O will eventually become franchise in a couple more years), and I continue to buy it every year. I just need year-to-year saves back so I don’t have to start over again.