.json and custom visuals with power bi theme possible?

Hi,

We have a .json theme file and can customise vast majority of properties of visuals which ship with power bi o.k e.g. background.

However, when try and set the propertries of a custom visual such as advance card as per below - no impact .eg. background property unchanged when import theme file unlike other visuals which change the background as expected.

Does anyone know if possible to use custom visuals in the .json theme file or not?

Just wondering if  possible to use custom visuals in the .json theme file? 

"advanceCard": {
"*": {
"labels": [{
"color": { "solid": { "color": "#063d73"}},
"fontSize": 14
}],
"background": [{

"show": true,
"transparency": 70,
"color": { "solid": { "color": "#Febe10" } }

}]
}
}