This app name is the technical id of the core Kibana app - timelion e.g. has a separate one. It is baked in very deeply into the code, so you would have to create a fork of Kibana, change all occurences and build Kibana yourself to make it work.
The most important ones are https://github.com/elastic/kibana/blob/6.3/src/core_plugins/kibana/index.js#L26 and https://github.com/elastic/kibana/blob/6.3/src/core_plugins/kibana/index.js#L46, but it might be hardcoded in other places too.