Actually you can do that by using the run_program syntax in updater-script to execute a shell script that moves/copies/pastes files while in recovery. But of course, you must extract the files that are to be pasted in somewhere (/tmp for instance).
Part of the updater-script:
package_extract_dir("stuff", "/tmp/stuff"); set_perm(0, 0, 0755, "/tmp/stuff/movefiles.sh"); run_program("/tmp/stuff/movefiles.sh");
The sample shell script can be like this (named movefiles.sh in this case):
#!/sbin/sh # Backup files cp /system/framwork/something.apk /path/you/want # Paste files cp /tmp/somethingssss.apk /system/framework/something.apk # Set back permissions (the copied file has the same permissons, but the new ones does not) chmod 644 /system/framework/something.apk
But remember, the EOL of updater-script and the shell script must be the same, in UNIX format, or else it won't work.