Unless you have a union that prohibits unapproved changes, the employer, by virtue of the employer employee relationship, can and frequently do change schedules after posting them.
The employer is under no obligation to consult with employees before making these changes, except in a represnted environment where shop stewards must be consulted before making schedule changes.
Most employment, without union representation, is at will employment and does not require consent or prior information before making changes to schedule.
HOwever, It is a good management practice to avoiding disgruntlement in the workplace, to announce upcoming schedule changes when ever possible. While it is not always possible, frequentl schedule changes shows weakness in the planning abilities of management; and to not announce it shows weak leadership and communications skills.
The only way you can deal with it is to first make sure you are informed, by reading your company bulletin board frequently.
The second thing to do is to see your manager on the open door policy to voice your concern, that you though you know changes to schedules are inevitabel, you would prefer more advanced notice in order to make changes in your schedule. Sudden schedule changes disrupt family life plans and visitatons by relatves who travel long distances to see you. Express your concern that not giving prior notice of a change, shows disrespect and lack of conern for the employees.
Make sure you are not trying to reverse the current change; and to accept the changes with grace and dignity.