Adding custom icons to the set of ABB icons

For our installations I require a very specific set of button icons on the OmniCore FlexPendant HMI. We are creating new sets of HMI's in AppStudio, however I do not directly see a method to import or add custom icons to the 'button icon' dropdown menu. 

Is there any way to add custom icons to Appstudio? Perhaps through modifying fonts in AppStudio assets?

Many thanks in advance.

Daan