Not that hard to do... make a nice looking interface add it to cache.
add something like this to rsinterface:
public static void Prayerswitch(TextDrawingArea[] TDA){
RSInterface rsinterface = addTabInterface(id);
addSprite(id, 1, "Location in cache");
Thats not all for client side but it is a start.
Then for server side it would be something like this:
clickobject.java:
case objectid:
c.getPA().showInterface(interfaceid);
break;
If u added buttons to the interface, Click one of the buttons and look the actionbutton id at the bottom goto clickingbuttons.java and do:
case buttonid:
c.prayerBook = 0;
break;
for another button:
case buttonid:
c.prayerBook = 1;
break;
Or make 1 button and add a } else { to the case with a boolean to check which prayerbook u has
Again this is not all do the rest urself
Iam not familiar with interfaces so forgive me if i did something wrong. ucan also try searching google for tutorials about adding interfaces.