How to "flash" a single updated file with CWM Recovery? I have modified certain .so library and want to safely flash it over existing firmware.
I see that incremental updates are possible (thinking of GravityMod2 3.0 to 3.1 to 3.2 update route); unpacking one of updates found on net, got this:

 inflating: changelog.txt           
   creating: META-INF/
   creating: META-INF/com/
   creating: META-INF/com/google/
   creating: META-INF/com/google/android/
  inflating: META-INF/com/google/android/update-binary  
  error:  invalid compressed data to inflate
  file #7:  bad zipfile offset (local header sig):  150328

 (seems like extra bytes in zip)


How do I prepare such updates?
After a number of attempts, found this distro at GitHub:
update.zip

Had to replace updater-binary to another version matching my phone (took it from verified and working firmware).

Next, modified updater-script to look like this:

ui_print("________________________________");
run_program("/sbin/busybox", "mount", "/system");
run_program("/sbin/busybox", "mount", "/cache");
run_program("/sbin/busybox", "mount", "/data");
delete("/system/lib/libXXXX.so");
package_extract_file("system/lib/libXXXX.so", "/system/lib/libXXXX.so");
set_perm(1000, 1000, 0644, "/system/lib/libXXXX.so");