You can use an app called Metamorph to change out the smiley .png images in the framework-res folder.
Metamorph is available on the market. You will have to find .png images or create them yourself that you'd want to swap out. The smiley names you'll need to replace are:
emo_im_angel.png
emo_im_cool.png
emo_im_crying.png
emo_im_foot_in_mouth.png
emo_im_happy.png
emo_im_kissing.png
emo_im_laughing.png
emo_im_lips_are_sealed.png
emo_im_money_mouth.png
emo_im_sad.png
emo_im_surprised.png
emo_im_tongue_sticking_out.png
emo_im_undecided.png
emo_im_winking.png
emo_im_wtf.png
emo_im_yelling.png
Find image to replace those, and on your computer, put them in this folder architecture:
new folder/framework-res/res/drawable-hdpi/image.png
Then, create a .thm control file (info here):
How To: Creating Metamorph Themes and save it in the root of the new folder you created (don't put it in framework-res folder). Use this tool to convert the .thm to an .xml file:
[RELEASE] Metamorph - Theme Control File Upgrader - xda-developers Make sure you remember the name of the theme you used in the .thm, and name the .xml file that name. For example, if you want to call the theme sms, make sure the .xml file is called sms.xml, and that inside the .xml, you've named the theme sms.
Zip together the .xml and the framework-res folder, and call the zip the same name you've used. (sms.xml).
Put the zip in a folder called AndroidThemes on the root of your SD card.
Open Metamorph on your phone, and click unzip a new theme, and select the .zip you just uploaded, and let it do the rest. You'll have to reboot for it to take effect.
If you don't want to mess around with creating your own theme file, send me the .pngs you want to swap out the stock smileys with, and I'll do it for you.