You'd have to edit the HIToolbox.rsrc to change the Trash icon. The file is located at /System/Library/Frameworks/Carbon.framework/Frameworks/HIToolbox.framework/Resources/HIToolbox.rsrc
Make a COPY of this file to work on. If you mess something up with it, you will not be able to boot into Aqua!
You'll need to download QuickConvert. You will need to drag the HIToolbox.rsrc file onto it. You will not get any dialogs saying that it is doing anything, but it is converting the file from a text file into a resource file.
After that, open the file into an icon editing program (IMO, Iconographer is the best one out there. This is a carbon version that works natively on OS X, too )
Once you drag the HIToolbox.rsrc file onto Iconographer, you'll get to see every icon that OS X uses. Edit away to your heart's content!
When you're finished, you'll need to drag the HIToolbox.rsrc file over QuickConvert again to convert it back into a text file from a resource file. This is very important to do! If you miss this step, even if you put the file back where the other one was, Aqua will not boot.
You should save the old HIToolbox.rsrc that you're replacing.
You'll need to be root to move the old file out and put the new one in its place.
As to the Trash on the Desktop - Tinkertool just sets a parameter in the Finder's plist, it doesn't do this directly. I'm not sure if the Trash icon is "stuck" in the lower left corner, or if you can move it around.