Edit code files and assets in the panel

Hi all –
I’ve got a peculiar setup with one of my clients where I’m permitted panel access but updating the code structure is a hassle every time. So I’m wondering whether it’d be possible for me as an admin to edit files in the /site/ folder (and others, like /assets for js and css) through the panel – whether by directly opening the files or uploading them through some custom solution.
Has anyone faced a similar problem and already come up with a solution? Any pointers would be appreciated.