Many apartment buildings cannot have structural changes after its construction. However, most of walls inside the apartments can be altered, but you have to check it out with the builder if it is a feasible and permissible task. If any damage is caused upon RCC (Reinforced Concrete Cement) structure, the building foundation can become shaky and weak; under worst-case scenario, the whole apartment building can even implode.
You should undeniably be reticent of the plumbing installations and electrical wires running inside the walls. You can consult the Structural Engineer before pounding the walls down to crumble. It takes a professional work to carefully dismantle the wall structure lest the adjoining apartment houses can feel the impact.