Once a credit package has been created and sold any edits to the Credit Type will retroactively apply to both those customers who already have the Credit in their account as well as those purchasing after the saved edits.
Any edits made at the Credit Package level - except the title - will not apply to those who have already purchased the credit package. The changes will only apply to those purchasing after the saved edits.
Penalty Fees can be retroactively updated for sold Credit Packages.
It is recommended that rather than changing the name of the credit package, you simply make an entirely new package. If you are merely changing the details of the credit package (price, expiration, etc.) you can just make those edits to the existing package.