Maybe it will help if I give more details.
I have my phone connected to my laptop via USB, and am using adb shell to gain shell access to the phone.
If I cd to /data, it looks empty. I know it's not empty, because one of my apps stores data there.
I have read elsewhere that there may be a version of su that I can download and install via adb push. Could I use this to gain root access via adb shell and then use that to remount the /data file system so that I could modify files there?
It just occured to me that maybe I could use adb push to overwrite the files. I'll look into that too, but I'm sure I would get permission problems with that too.