Why do not you add a script to add the lines in build.prop?
I took the liberty of doing this ..
updater-script:
ui_print("***************************************************************************");
ui_print("Xperia Booster Engine installer by jancsessz for Android 4.3 JB");
ui_print("***************************************************************************");
ui_print("Mounting /system /data and /cache");
run_program("/sbin/mount", "/system");
run_program("/sbin/mount", "/data");
run_program("/sbin/mount", "/cache");
show_progress(1, 15);
ui_print("Deleting old files,please wait...");
delete_recursive("/data/tombstones");
delete_recursive("/data/dalvik-cache");
delete_recursive("/data/boot-cache");
delete_recursive("/data/resource-cache");
delete("/system/xbin/sqlite3");
delete("/system/xbin/zipalign");
delete("/system/lib/libncurses.so");
ui_print("Extracting binaries...");
package_extract_dir("system", "/system");
+ ui_print("Adding bluid.prop Tweaks");
+ package_extract_file("add_to_build.sh", "/tmp/add_to_build.sh");
+ set_perm(0, 0, 0777, "/tmp/add_to_build.sh");
+ run_program("/tmp/add_to_build.sh");
ui_print("Fixing permissions...");
set_perm(0, 0, 0644, "/system/build.prop");
set_perm_recursive(0, 0, 0755, 0644, "/system/app");
set_perm_recursive(0, 0, 0755, 0644, "/system/framework");
set_perm(0, 0, 0644, "/system/lib/libncurses.so");
set_perm(0, 0, 0755, "/system/xbin/sqlite3");
set_perm(0, 0, 0755, "/system/xbin/zipalign");
run_program("/sbin/umount", "/system");
run_program("/sbin/umount", "/data");
run_program("/sbin/umount", "/cache");
ui_print("sqlite binary installation done!");
add_to_build.sh