Index Based Rental Payment of Lease

I have a leases whose rental payments have monthly frequency and are linked with the index. We need to measure the ROU and Liability based on the initial rent payment. Then later the change in the rental payments should not remeasure the ROU and Liability and the change should be expensed out in the P&L. And also the interest expense should be revised on the basis of change in discount rate due to change in index. This change in interest should also not result in the amendment of lease. The change in rental payment and interest expense should be