Yes, this is possible by means of an addendum to the Participation Agreement. There is currently no charge for this.
If an employer decides to change or add a different tier with different contribution rates than what they have already agreed to, they will need to contact employer support on 0 330 100 3399 to request an addendum to the contract.
If/when this is approved they should alter contributions by changing the Employer Contribution (ER CONTS) amount and Employer Contribution Rate (ER CONT %) within the payroll file.