Hi Alex,
it is not possible to add and remove constraints in acados after creating the solver.
This is because the allocated memory is dependent on the dimensions of the problem, part of which are the number of constraints at each shooting node.
What you can do is set a maximum number of inequality constraints when creating the solver, where most of them are trivial and they become nontrivial (by setting parameters and/or bounds) when there is an obstacle.
Best,
Jonathan