Hey, great work so far!
Don't be shy! How do you think other developers (beside of kartu, who is a naturally born Sony hacker

) started?
For instance: see my post about the FSK-Test-Environment (or short SIM)
here
And not to anticipate
kartu, but IMHO your save/load settings code as well as this CSS manipulation will have the best chances to be integrated into "official" PRS+
But this is the fine thing on GPL code, each and everyon has the chance and the rigth to use and change the code to his liking, but will have to share his results to the public.
So again, don't be shy and push what you have to your repository.
So maybe someone can lend a helping hand.
Reagards
Mark
PS: if your button is a descendant of "radio-button" it should be using your mentioned "state-var". See if it can be defined in the xlm's "<model>" section.
For the Calculator I've done it like this:
Code:
<model>
<variable id="BASIS" value="dec"/>
<variable id="TRIG" value="deg"/>
</model>
....
<radio id="RBUTTON_HEX" variable="BASIS" on="hex" active="true" text="HEX" left="040" width="55" top="0" height="30" do="setNumberBase"/>