Followed the directions posted in:
Editing Rosters and Player Ratings in Football Mogul by Clay Dreslough (Updated September 24th, 2020)

I attempted option 3) Edit the raw data in Football Mogul's "Stats" folder (in the "Input" folder;
e.g. "C:\Sports Mogul\Football Mogul 20\Input\Stats"). Then use the "Create Historical Database"
or "Create Modern Database" buttons in the Advanced Options Dialog.

I modified the month and day of birth for every player in Input\Stats\2019_rosters.csv to Feb 22.
(I want player aging to take place between seasons, I can only get this by changing the players birthday)

Started a new game in the current year (NOT using fictional players).

Ran Tools->Advanced Tools->Create Modern Database.

Checked the Databases\Universe-2019.dat file. It was modified. It is 434 KB ~ 400 KB smaller that the original Universe file.

Closed FB Mogul.

Started a New Game in the current year (NOT using fictional players)

Checked out the players on the Cardinals.
1) All had a Cap Impact of $495K. In fact, all players on all teams had that same Cap Impact.
2) The Arizona players in the 2019_rosters.csv were not on the Arizona team.
3) The Arizona players in the 2019_rosters.csv were not on ANY team.
4) Of the 1368 players in the newly started game only FIVE were in the rosters.csv file.
None of the five were on the team they were on in the rosters file.

There appears to be something additional that needs to be done either in editing the rosters.csv file or after editing the rosters.csv file.

Other issues with the rosters file:

Are the players required to be in a specific sort order in the Input\Stats\2019_rosters.csv file?

Near the bottom of the Input\Stats\2019_rosters.csv file, there is a separate section that contains Free Agents.
There appear to be three additional fields here. One is labeled "Retired". The other two are not labeled but some
contain data.

Is this section needed?
What are the unnamed columns?
Are these players supposed to show up in the Mogul Free Agents display?
Is there a specific sort order required?