If my airpods case is damaged, can i change charging case with the same airpods or do i have to buy another pair?

You can buy another charging case and pair your AirPods with the new case.

The AirPods cases are interchangeable, if that is your question.

Apple does have available replacements:

AirPods Repair - Official Apple Support

The cases are interchangeable, so you can absolutely change just the case and keep the original AirPods. You would have to go to the store for this. The staff will pair your AirPods with a new case and you just have to wait for approx. 30 minutes before you can use them.

Hope this answers your question. 😊