How can I trim shapes that overlap the page?

Question

I am working on a 270 page holiday brochure. I usually work with Photoshop, but I know this isn't ideal for brochures, so have been working along side another designer with InDesign. I've picked up nearly everything to get me going which is great. However, I am stuck on the best practice for the background.
The idea is that every page with a hotel will have the same background style, which is made up of a couple of circle shapes that are slightly different shades. The circles go off the edges of the page, to basically just form a curve across the page. Each different destination will have these shapes in different colours, so the client would like to be able to change the colours around once I hand the brochure over to them.
I can work with what I have now, but it is looking a bit ugly having huge circles exiting the edges of the page in "Normal" view.
Is it possible to cut off the rest of the shape which isn't inside the bleed?

Answer 1

And: you need a group inside a rectangle to drag something new inside of the rectangle from outside using the Layers Panel (as shown in my post #7). So the advice Peter has given is a essential one.
Even if you currently need one single object inside the main rectangle, I would suggest adding a group first.
A second object could be a tiny rectangle without a fill and a stroke color. So later you can add other objects inside by using the Layers Panel and dragging objects to that group.
Removing the second object from the group when inside the rectangle will be no good idea, because the groupness will be destroyed in the same moment you remove an object in a two-object-group. You will bot be able to add another object by dragging.
Said that, by scripting we could generate a single-object group by having two objects in a group using the following script snippet code (ExtendScript/JavaScript). Just select one object or more and run the following code:
//ExtendScript (JavaScript)
//Remove all selected objects:
//DESCRIPTION:By selecting all objects in a group BUT a single one, the remaining object will stay as part of a group!
//Uwe Laubender
if(app.selection.length === 0){
    alert("Nothing selected. Try again.");
    exit();
for(var n=app.selection.length-1; n>=0; n--){
    app.selection[n].remove();
alert("All selected objects removed.");
Before running the script snippet:
After running the script snippet:
As you can see the rectangle that is left remains inside a group. What we have here is a single object "group".
And you can always drag objects inside that "group".
Uwe