First of all i want congratulate you, is the best plugin for wordpress chess on!
I are the site administrator http://www.g-sei.org/ and use your plugin pages http://www.g-sei.org/?page_id=1487
To display properly the pieces, i copied the folders USCF, merida and another that i can not remember. For each update of the plugin, however, I are forced to copy everything all the time.
You can find a solution?
I’m sorry for my bad English (accidenti, ma guarda te, provo a parlare in inglese ad un’altro italiano come me! Chissà che risate!)
Everything is possible, but what you are asking is currently not planned.
The plugin is intended as a ready-to-use solution for people that dont want to fiddle with files, configurations and programming. As such it has limited options.
You probably should consider a different solution, such as not using the wordpress plugin, but installing the whole pgn4web software on your server, create the page you like better and use it on your wordpress pages. Not to hard to do for someone with programming skills.
We can have the conversation on the g-sei.org forum if you prefer talking in Italian.