Dear lifella1948,
This depends on may factors. I believe if either you or she still lives in the original state where the divorce took place, then yes you have to go back to that state. If not, then you will have to petition the state where the children currently live for reduction.
You may or may not get the reduction. Some courts would consider that a voluntary reduction in pay, since you are capable of working and are choosing not to. They may feel that you CAN support your child(ren) at the current level and therefore should continue. If the court REALLY wants to be a jerk it could say that you can get a job for XY per year AND still draw your retirement, so she deserves a raise not a reduction. It is hard to predict.
In my opinion, you should seek a professional help of attorney post retirement and this is a matter of domain expertise.
I hope the above helps...
Regards,
Financial Advisor
Technical Analyst in Financial Markets -- Experience of more than 10 years in consulting