Patch Phone Editing the Lock Screen
From WebOS Internals
Editing the Lock Screen
Changing the Lock Screen background is easy as well. In fact, the image resides in the same directory as the dialer's background.
The file that you'll want to edit is the backdrop-firstuse.png file.
Simply follow the directions above for copying the files out and back into the /usr/palm/applications/com.palm.app.phone/images/ folder, reboot and your lock screen background is changed.
This video helped make each step simple to follow 
This is what I changed my theme to:
cp backdrop-firstuse.png backdrop-firstuse.png.old
cp backdrop-firstuse-scroll-fade.png backdrop-firstuse-scroll-fade.png.old
cp list-section-line.png list-section-line.png.old
Next we'll need to copy (cp) the files to the location of the USB drive so that we'll be able to edit these files:
cp /usr/palm/applications/com.palm.app.phone/images/backdrop-firstuse.png /media/internal/
cp /usr/palm/applications/com.palm.app.phone/images/backdrop-firstuse-scroll-fade.png /media/internal/
cp /usr/palm/applications/com.palm.app.phone/images/list-section-line.png /media/internal/
Now click on the USB icon on the Pre's notification area, switch to USB Storage mode.
You can now copy the files off of the Pre and edit them any way you want, just make sure they have the same properties as the orig (transparency, size, file extention, etc). I didn't create these image below, they are just edited from the Palm Pre. You can use any 360 x 420 PNG to achieve these results.
Once they are edit to your liking, copy the files back to the Pre in USB mode with the same file name.
Eject your Pre from your computer, wait for Wifi to log back into your network, and SSH into the Pre again. Your old window probably timed out by now so you can close it.
Step 4 (Last) Now we'll need to get the files (all 3 if you edited them) back to the correct location, so we'll use the copy (cp) command to do this.
cp /media/internal/backdrop-firstuse.png /usr/palm/applications/com.palm.app.phone/images/
cp /media/internal/backdrop-firstuse.png-fade.png /usr/palm/applications/com.palm.app.phone/images/
cp /media/internal/list-section-line.png /usr/palm/applications/com.palm.app.phone/images/
(be sure to mount/remount before rebooting)
Hit ENTER then type reboot and hit ENTER again
--Chrisana33 00:39, 7 August 2009 (UTC)Chris