There are several ways you can achieve your goal. I describe one of them here. I do this under the assumption that you are using Windows and 7-zip is installed on your system.
Step 1 (decompress KoboRoot.tgz)
I guess you have the file KoboRoot.tgz of FW 2.8.1. Decompress this file twice (with 7-zip). First you get KoboRoot.tar, if you decompress KoboRoot.tar you get some folders with subfolders and files.
Step 2 (edit two files)
The two files we are looking for are
[CODE]usr\local\Kobo\udev\usb
etc\init.d\rcS[CODE]
Edit these two files (replace all occurrences of KoboRoot.tgz with xKoboRoot.tgz).
Step 3 (create the paths C:\KoboRoot\etc\init.d and C:\KoboRoot\usr\local\Kobo\udev)
-Open the command prompt window (cmd) and execute the following four lines (press ENTER after each line);
Code:
md C:\KoboRoot\etc\init.d
md C:\KoboRoot\usr\local\Kobo\udev
Of course, you can create the folders also with explorer, but this is tiresome. (Upper and lower case is important!)
From now on we use the explorer.
Step 4 (put the modified files to their new locations)
Copy the rcS file to C:\KoboRoot\etc\init.d, and copy the
usb file to C:\KoboRoot \usr\local\Kobo\udev.
Step 5 (compress)
Navigate to C:\KoboRoot. Select etc and usr. Right-click and select 7-zip > Add to archive ... Choose Archive format: tar. Press OK.
Right-click in the explorer on KoboRoot.tar, select 7-zip > Add to archive ... Choose Archive format: gzip. Change the archive name from KoboRoot.tar.gz to KoboRoot.tgz. Press OK.
Step 6: Copy the newly create KoboRoot.tgz to the .kobo folder of the device.
From now on your device might download the update files from Kobo, but it will not install them. If you want to install an update file rename it to xKoboRoot.tgz.
If you want to install a pached file via KoboRoot.tgz, or anything that uses a KoboRoot.tgz file, you have to rename it to xKoboRoot.tgz.
Be aware that when Kobo prepares an update, it puts apart from KoboRoot.tgz also a folder "update" into .kobo. It is important that you delete this folder before you install anything via xKoboRoot.tgz.