Players cannot do overrides in roster only leagues. Only drafting, contracts and depth chart.
The opportunity to manage how the roster is used on the field is absent.
Directly, there is no actual roster management in Roster Only leagues.

I consider not being able to manage the roster via overrides in roster only to be a fixable bug :)

I'm in 2 roster only leagues, and I'm able to set Depth Chart Overrides in both of them.