Not currently, but this will be possible soon. The technology for syncing the full code editor (not just the one to the left of the Font property group) has already been developed. See the ability to import raw CSS into the Ui via Packs > Import > CSS stylesheet for instance. And in the not too distant future there will likely be a ‘Synced Code’ and ‘Unsynced Code’ tab in the full code editor view.
The unsynced tab will function how the current full code editor functions. The synced tab will provide a way of editing the CSS added via the UI fields without restriction. Although having said that, it may only be possible to edit the CSS within a single folder at a time. This would be for performance reasons – to ensure that Microthemer doesn’t have to crunch too much data when thousands of selectors are present.
Does this proposal make sense to you? And would it satisfy your requirements?