There are several ways to actually change permissions on the file, but the safest (and non permanent) way is to use root explorer. ES *does* have an option to use it in root mode (menu->settings->root options-> check "Root Explorer"), BUT I've heard it can cause all kind of problems.
If you have both a terminal emulator and busybox installed, you can definitely do what you need to do. It's more time consuming, but it *will* work. There are many ways to do what you want, including actually changing permissions, but that's not a great idea.
So, install a terminal emulator if you don't have one:
Android Terminal Emulator - Android app on AppBrain
Open it, and verify you have busybox by typing "busybox" without quotes, then enter. If just says anything about not being able to find it, it's not installed. If you get some general information, then a list of commands, you're good. If you need it, here it is:
BusyBox - Android app on AppBrain
Now, you should modify a widget.txt file either from your phone or from your PC. Be careful when doing it from your computer. If you have windows, and you make it in notepad, you could end up with junk character. Make sure to put the widget.txt file on /sdcard. You can copy it there from where ever you have it using ES.
Once that is done, open the terminal again, and type "su" then enter. The prompt should change from $ to #. type the following commands:
cd /system/customize/
cp /sdcard/widget.txt ./
cat widget.txt (note: the output should be the contents of the new widget.txt)
If you get any errors or anything, do this command then try the cp command again:
rm -f widget.txt
Once you have copied the file, type:
ls -l widget.txt
the first column should look something like this:
-r--rwxr-x. The second, third, and fourth characters (-r-) are the most important, as they generally end up getting reset to --- when you copy a file from elsewhere outside of /system. It basically means the system won't be able to read the file, and it will be useless. If you see something like that (----rwxr-x), run this command:
chmod u+r widget.txt
then check again. You should see -r--rwxr-x. If that's the case, you're done.
I know this is very complicated if you've never done anything from the command line, but it *does* work and it's free.