Thank you for contacting Syncfusion support.
Please find the following responses for your queries.
Yes, it is possible to customize the horizontal header label and for the same we have prepared the sample which can be download from the below location.
Yes, it is possible to customize the appointment editor. In default appointment window it is not possible to customize the resource fields, therefore in the above sample resource fields are added in the custom window where you can customize the resource fields as per your requirement.
We are unclear about this requirement, kindly share more information like code example/sample/image/video demo which clearly depicts your requirement to serve you better.