Now I found some time to test.
JSON-Format was already correct, but then a modifier of type “Decode a JSON string” is required.
With this I got form a csv like this:
host,customvars
linux,'{"os":"Linux","description":"good"}'
windows,'{"os":"Windows","description":"bad"}'
Two host like this:
object Host "linux" {
import "Default Host"
vars.description = "good"
vars.os = "Linux"
}
object Host "windows" {
import "Default Host"
vars.description = "bad"
vars.os = "Windows"
}