How to register a new texture for an unit's order icon?

[Wakke]

Hello, does anyone know how to make it so you can refer to a custom texture for a custom order button on a unit?
So, for example, I want to replace the icon of overcharge, I know that my textures should come in the folder:

Textures\ui\common\game\orders

but how do I refer to them in the unit blueprint?:

OrderOverrides = {
RULEUTC_ProductionToggle = {
bitmapId = 'XXX',
helpText = 'Detonate on death',
},

So the part indicated with 'XXX'. How can I go about that? I guess the Nomads did something like this, but I can't find the source code?