"We want to be the top package-delivery option, and we want customers to take a fresh look at doing business with us," she said.
Manabe called the changes "a game-changer" in the shipping marketplace.
Postmaster General Patrick Donahoe said that "a lot of operational investments have been made over last couple of years" that make it possible for these changes, including a focus on technological issues to handle growing online purchases.
He continued on Wednesday to push for that type of "flexibility."
Top postal service officials argue that they need Congress to pass comprehensive legislation to allow them to get back on solid financial footing.
Donahoe has pressed to cut Saturday mail delivery amid a seven-year decline in first-class mail volume, but keep delivering packages, where the revenues have grown, for six days.
The most recent financial report showed that package delivery revenue was up 8.8 percent, compared to the third quarter of 2012, boosted by an increase in online shopping. Overall, the package business has grown by more than 14 percent over the last two years.
The agency said Friday that it has lost $3.9 billion so far this year and is likely on track to lose $6 billion.
Still, that is well below the record $15.9 billion the agency lost in 2012.
The service has struggled financially because of a legal requirement to prepay billions into retiree healthcare funds. Without the payments, the agency would be making a profit.
On Monday, Sen. Bernie Sanders (I-Vt.) argued that the service would have posted a profit for the past three months without the requirement to deposit $5.5 billion a year into the retiree fund.
Priority mail, which ranges from one to three days, will include $50 or $100 of insurance coverage depending on the payment method, such as whether a customer brought it to a retail counter or it was paid for online.
The last time changes were made to priority mail was about six years ago when the flat-rate boxes were first introduced, officials said.