Free Tier to Paid

hello,

if you are asking whether it is mandatory to change the instances after migration to pay,

I believe no, and there is no categorization for the services to be migrated, it's only the type of usage you are doing but whatever you are working it's the same

hope my answer helps

Hello.

It is possible to change the settings of an existing EC2 instance to an instance type that is not eligible for the free tier.
Specifically, it is possible to change from t2.micro to an instance type such as m6i.
However, depending on the destination instance type, driver installation etc. may be required.
https://repost.aws/knowledge-center/migrate-to-gen6-ec2-instance
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/migrating-latest-types.html

No, you do not have to change your instance type. When Free Tier offer runs out, all instances begin billing as paid tier.

This link provides information to track your Free Tier usage.
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/tracking-free-tier-usage.html