The reason it shows it is because the username and the display name are not always the same. You can remove them if you wish by going through the source files and finding them but I seriously can't imagine it's worth it.
You can't easily get files out the ya file. However, if you download the *safe* download package of the forum from here all the files are already extracted for you so just upload them from there.
SMF will be coming out fairly soon and that has a "smiley mod" built in for you if you still want to smiley mod