Do I have to get whitelisted again?
I want to change my minecraft account name, does that mean I have to be re-whitelisted?
No, every account has a universally unique identifier (UUID) which is used for whitelisting. This was added in 1.7.5.
Some more info from before the change: https://bukkit.org/threads/psa-the-switch-to-uuids-potential-plugin-server-breakage.250915/
TL;DR you will be fine