Hello @sswen20,
Regarding your main issue of not being able to add ConstantThrustManeuver during propagation, it is indeed not possible at this moment. They are considered in the org.orekit.propagation.numerical.NumericalPropagator.Main#setUpInternalDetectors method which is in fact called before propagation (see createODE(integrator); in org.orekit.propagation.integration.AbstractIntegratedPropagator#integrateDynamics for reference).
You might be interested in the following thread which covers a station keeping case using low thrust : Station keeping using low thrust - #20 by Vincent. Full code snippets are provided in both Python and Java so it might give you some insights on ways to do what you want.
Cheers,
Vincent