The flag on the tflag or tnational smiley can be customized by adding #w and then the country code. For example, (tflag#wgb) or (tnational#wgb) will show a UK flag. See the Flag article for available flags.
The smiley on the tsmile smiley can be changed by adding #tsmile to your desired smiley. For example, (cool#tsmile) will show the cool smiley on the tshirt.
The tshirts and tshirts2 smilies also have different versions available: