You can customize it by changing: /etc/mycroft/mycroft.conf
The settings you put in there will override the defaults. You can see defaults at:
This file has been truncated.
// Definition and documentation of all variables used by mycroft-core.
// Settings seen here are considered DEFAULT. Settings can also be
// overridden at the REMOTE level (set by the user via
// https://home.mycroft.ai), at the SYSTEM level (typically in the file
// '/etc/mycroft/mycroft.conf'), or at the USER level (typically in the
// file '~/.mycroft/mycroft.conf').
// The Override: comment indicates at what level (if any) this is
// overridden by the system to a value besides the default shown here.
// Language used for speech-to-text and text-to-speech.
// Code is a BCP-47 identifier (https://tools.ietf.org/html/bcp47), lowercased
// TODO: save unmodified, lowercase upon demand
// Override: none
// Measurement units, either 'metric' or 'english'
// Override: REMOTE
For example, you can fill your /etc/mycroft/mycroft.conf with