Yes, REAPER is rather flexible in customization, build-in or with add-ons (BTW SWS is the most popular). But I don't recommend modify anything at the beginning, f.e. don't install "Sonar like" schemas. Changes/flexibility was proposed by particular users, sometimes for particular purpose. Sure, REAPER can NOT work exactly as any other DAW, even with all its flexible.
Just learn how to do things "REAPER way". Everything is logical and consequent there, the logic is just different from other software.
A track icon is a "decoration element" of "Track control". So, it has no own definitions for mouse operations. Almost everything related to particular interface element can be found in its context menu. In short time, once you learn which interface elements exist, it is rather simple to navigate throw "menu jungles".
But menus is not the only way to do things in REAPER... All operations are "Actions". You can open the Actions dialog and search there (f.e. for "track icon"). Once you have found the Action, there are options how you can call it. You can define shortcut (in the same dialog), add it to toolbar (there are many...) or assign it to some mouse modifier (in Options). So, you can assign it to "Ctrl+Shift+Dbl. Click" for "Track control" area.
Still inconvenient? Why set colors/icons manually every time? Yup, you can set them automatically based on the track name. With SWS extension, "Auto color/icon" enabled and your own rules.
As the result, once you name a track "Gtx 3" its color and/or icon is changed to "Gtx 3" specific, or into "Gtx" (if you don't have "Gtx 3" specific).
If automatic is not what you want... there are still other options. F.e. you can create a toolbar with a set of particular track icons, when you click on a icon there it sets current track icon (color, name, whole track template, etc.) to that one (you will need SWS and a bit of time to prepare such toolbar).
So no, you can't assign it as dbl. click on the icon only, but there are many workarounds