Fork this project and make your changes, then send a pull request for us to review. Please describe your changes in depth.
The simplest way to implement new endpoints is to get the JSON data from the API manually and paste as JSON in Visual Studio. Then change the class to implement DtoProviderBase and change all properties to use Get() and Set(value). Values that don't implement Get() and Set(value) will not be sent to Visma.net during ADD or UPDATE.
When you implement a new endpoint you can just paste the JSON as classes and use this regex to create a good basis for the correct data class.
FIND: ([a-zA-Z\?<>]+) ([a-zA-Z]+) { get; set; }
REPLACE: $1 $2 { get { return Get<$1>(); } set { Set(value); }