Here is on of the possible solutions:
1) first find data json with type html
2) transform json value child
val parsed = JsonParser.parse(jsonString)
def encode(s:String):String = s + "encoded"
private def encodeValue(dataObject: JValue) = dataObject.transform{
case JField("value", JString(value)) => JField("value", JString(encode(value)))
}
val newJson = parsed.transform({
case dataObject @ JObject(fields) if fields.contains(JField("type", JString("html"))) => encodeValue(dataObject)
})