How do I change an icon in the notification area?

I've been watching this post for days, hoping somebody else would take this and run with it. Nobody has, so I will do it, however reluctantly. @Nisko: the notification area exists primarily to "display icons for system and program features that have no presence on the desktop, such as battery level, volume control, and network status." Read about it in this nice MS article entitled "Notifications and the Notification Area." Alas, you cannot just drag icons of your choosing into this area. The underlying programs must register with the notification area as part of their installation, after which they either will (or won't) show up there. It's not up to you: it's up to the software's developers, to do the work necessary to make this happen. Thus, alas, I must tell you that "you can't get there from here!"
Sorry to be the bearer of potentially bad tidings.
Best wishes,
--Ed--

Hello Nisko,

Do you mean you want to add and remove items from Quick Launch?

If so, you would just need to add or remove shortcuts you want from the Quick Launch folder.

Add or Remove Quick Launch toolbar in Windows 10 | Windows 10 Tutorials

Add Quick Launch to Send to Context Menu in Windows 10 | Windows 10 Tutorials

Just to clarify, please post a screenshot of your taskbar with the area you want to change circled.

Like Eddie said, I think he's right. The Notification Area & System Tray are the same thing.

It sounds like you are referring to the area with the widest area (where your running programs are listed). Refer to the picture.
If you're referring to this area (where it shows "Foster The People" & Google Chrome to its right) then you must run the program itself to show in that area. That area is temporary.

You probably want to add a permanent icon, which would be in the QuickLaunch area, correct?

The part in the middle is now called the TaskBar. Icons in what used to be called the System Tray are now also called the TaskBar as well in many circles.

I refer to the entire bottom as the Taskbar, and the icons to the right are in the Notification area etc.

Because that`s what they do, they notify you of something. For example, Your Geforce Experience icon notifies you when there is a driver update, if you have it set to do that.

Core Temp shows you your CPU temps etc

(I thought the TaskBar is the whole entire thing itself, including the Start Button & the Notification Area. If you right click in the center part of the TaskBar, the lastly listed option is "Taskbar settings", yet if you also right click on the clock, you will see "Taskbar settings" listed last. Doesn't this imply that the whole thing is the TaskBar?)