Corrections or modifications of an employer's payroll may be taken into account within two years after the computation date for the purpose of a reduction or increase in the employer's rate. When an adjustment is made in an employer's payroll or in an employer's average quarterly decline quotient after rates have been assigned, the adjustment may not alter the position of another employer on the schedule or the contribution rate of another employer. The employer for whom the adjustment in decline quotients is made shall be placed in the class in which another employer with the nearest similar average quarterly decline quotient is placed.