Nonqualified deferred compensation plan permits distributions in form of either lump sum or installment payments over period of a maximum of 10 years. What issues arise if plan is amended to permit distributions in installments of amounts selected by participant (i.e. 10,000 the first distribution year, $5,000 the next two years, and none the fourth year, etc.)?

Well if it's amended before the participants have earned the compensation being deferred, there are no problems. Otherwise, there is a constructive receipt issue when the participant has a right to get the money.