!Must be on Active Roster Designation!
 

Does anyone understand why some players have an exclamation point ! after their name and are designated as "Must be on active roster or IL all season?" What is up with that?

Is there any way to customize rosters easily without having to go through the whole Free agent/Waivers process?

! were selected in the Rule five draft and have to be on the roster or returned to the team they were drafted from.

You can export and import rosters from the League Settings > Functions page. That will let you edit them outside the game.

Here are the MLB basics of the Rule 5... https://www.mlb.com/glossary/transactions/rule-5-draft