If you have a project and need to discount the hourly rates, this can be done in Project Profile >> Estimated Work.
# Profile * Estimated Work * Modules * Team
The right column has the discount functionality:
When applying the discount the rates will be updated and you will have the option to confirm or deny the discount.
Hourly discounts can be useful in a variety of way. We use them for our Maintenance contracts because we give various discounts for purchasing buckets of hours up front. Discounting the rate is easier than setting up a bunch of different default work type and rate combos for each contract.
Unfortunately, there is not great way to remove a discount. Intervals will accept a markup/premium by enter a negative discount (like -5%), but that won't get back to the original. Manually editing each rate is probably the best bet.