Add conversion "on the fly" for certain existing Media models?

[Braunson]

I want to add a conversion for a specific media model at a certain time (i.e. Person model is updated with a media_id, I have a listener that on saving of that eloquent model dispatch a job that does this and ideally would generate a conversion just for that one specific media item.

$media->addMediaConversion('largebox')
    ->format(Manipulations::FORMAT_PNG)
    ->fit(Manipulations::FIT_CROP, 4096, 2048)
    ->performOnCollections($diskName);