Hi @sorosoro,
At this time, the only way to customize Simple Search is by using Specify 6.
Modifying the XML that defines the ExpressSearchConfig directly is not recommended or supported. It is permitted so that advanced users can import pre-configured search configs for users. Manual edits will be overwritten automatically by Specify 6 and will behave unpredictably.
When you configure Simple Search in Specify 6, it automatically updates the ExpressSearchConfig app resource owned by your user. This is how it is carried over from the Specify 6 configuration.
If it cannot be added using the Specify 6 user interface, it is not currently supported. This means that if origElevationUnit cannot be added in the 6 configuration tool, it cannot be added by modifying the XML manually.
In short, you should not modify the XML in Specify 7. We only support configuration of Simple Search in Specify 6 at this time, however we have an issue on GitHub to add this ability to Specify 7 in the future.
Thank you!