Inside of directory genieacs-gui/config we find YML files that are used for tinkering the GUI options of GenieACS.

parameter_renderers.yml

In parameter_renderers.yml, you can change how a certain parameter is rendered in the GUI with some Ruby code. Have your custom functions in a file under config/parameter_renderers directory and reference them in the YML file. See the sample renderer for the uptime parameter.

parameters_edit.yml

The file parameters_edit.yml lets you specify what values (or ranges in case of int types) are allowed editing a parameter. This will modify the dialog that pops up when you click "edit" link in the GUI.