Technically, it seems possible to share Syncthing’s own home folder from Android to other devices without root because the app itself does have access to it (see https://forum.syncthing.net/t/how-to-share-syncthings-own-config-folder/19642/10). While not the best practice, you could then edit the file remotely, wait for it to sync back, then restart Syncthing on Android which will then use the modified configuration.
The same applies to the key and cert files, although I don’t really know what will happen if you delete/replace those while Syncthing is still running.