if you want to change a person's pay rate or commission structure in New Hampshire, is there is required notice period for such action? thanks...

Not to my knowledge. In most states, the only requirement is that the employee receive notice prior to working any hours at a lower rate, and a notice above the time clock: "Effective today, the new rate for employees in such and such a job is $x.xx" will suffice.

However, NH tends to play against type, so you might want to place a quick call to the state DOL to be certain.