If like me, having multiple options for one loco or unit drives you up the wall on your quick drive menu, you can now sort it out.

For example, if you have bought the ECML: York to Peterborough, you will notice that the passenger consist for the Class 47 is:
Cl 47: Class 47 BR Blue + 9 Mark 1

So, as an example, let's sort this out, in two possible ways...

When you have downloaded TS Tools (see below for the link), open it up and navigate to "QD Files", then "Check or edit existing...", as below:

Then make sure that the file location at the top is your assets folder - this would usually be C:\Program Files (x86)\steam\steamapps\common\Railworks\assets. When this is done, click "Find all consists in folder" (I think!) - on smaller screens it is the top button saying "...consists in...". Click this and get a cuppa - if you have lots of DLC and third-party things, this could take some time! See again the picture below:

When your list of assets has fully loaded, check if anything hasn't appeared in the list. This would usually be because of the way certain apps extract .ap files (the file type which is used to compress a number of routes and stock when you install them). If this happens - the consists do not show from a .ap file - then don't worry, you can quickly edit this from TS Tools. Just go back to the main menu, and click on "Options", then "Make files in Selected Folder Read/Write". This will convert all your files in your assets folder to read/write, so they will appear in your QD consist list. Then go back to the QD consist list, and click "clear grid", then "...consists in..." again, to reset the list including everything.
Now you have your full list of what appears in your QD menu, you can now start editing it. Let's take the "Class 47 BR Blue + 9 Mark 1" from earlier. If we select it with our mouse, and click "Edit selected QD consist" at the top, we see this screen:

Now we see what makes up this consist. If we go to the bottom right hand corner, we see that the 'Loco name' is "Class 47 BR Blue + 9 Mark 1". However, we don't really want this, so let's change it to "Class 47". However, to distinguish it from the other entries under "Class 47", which already exists, let's add something in the 'Display name' - for the purposes of this, let's just add TEST after the display name. So, it now looks like this:

Then click "Save As", then "No" (we don't want a copy of it - we want to replace it).
You can do this for pretty much anything (with one major caveat - see below), so after you've done this, you can open Train Simulator, go to settings (top right corner), then Tools and Clear Cache. This will mean what you changed will appear after it reloads. Et voila - the "Class 47 BR Blue + 9 Mark 1" has disappeared. And if you look under the Class 47 tab, you will find our renamed consist.
We see our new consist appears nicely in the list there. Of course, you don't need to add TEST after every change you make, but, for instance, if you want to get rid of the "Class 158 DMU" (only used for the trains on the Liverpool to Manchester route), then you can add "(LivMan)" after their display name, for example, to avoid confusion with other Regional Railways Class 158s.

Of course, you can do this to the "Class 43 HST + 8 Mark 3" from the ECML: York to Peterborough as well - just rename it to "High Speed Train" and you can combine it with all the other HST options.

The other way is slightly more complicated and involves code!
If we try this second method for the same consist ("Class 47 BR Blue + 9 Mark 1"), then we can compare.
Thus, if we go the file location for the consist (Railworks/Assets/CreativeRail/EastCoast/Preload), the consist (or .bin file) we are interested in is the 47 BR Blue consist. If we right click, and select "Open With", it will give us some options. Select TS Tools, or, if it doesn't appear, "Look for more apps on this PC" (then go to C:/Rail Utilities/TS-Tools/TS-Tools.exe). This will open the consist as follows:

Now we need to scroll down a LONG way, until you see "<Loco name>" - generally this is about 70% - 80% of the way down. Then, look in particular at this line of code:
<English d:type="cDeltaString">[LOCO NAME]</English>
The Loco name in bold will be whatever appears on the QD menu. So for example, for this consist, we can change it to:
<English d:type="cDeltaString">Class 47</English>
Which means it will be shown in game under the Class 47 option.

If you want to also change the consist name as well (the specific bit that comes up as one of the options after you select what train you want to drive), then scroll a bit further until you see "<DisplayName>". Then look at the line:
<English d:type="cDeltaString">[CONSIST NAME]</English>
Then you can change the Consist name (again, in bold). So for this, if we want it to be specific, we can change it to:
<English d:type="cDeltaString">Class 47 BR Blue + 9 Mk1 (York to Peterborough)</English>

So the new code for these bits will now look like this:

Then hit Ctrl + S to save. This will make the previous version of the consist redundant, so delete the .bak file that has just appeared in the PreLoad folder, as below:


Then open TS (it is suggestable to clear the cache - see above) and you're on your way.

The one downside to this is that SOLUTION A won't work with everything. This is because the 'Loco name', the name which appears in the QD menu, needs to be set up previously, which can only be achieved from SOLUTION B. Therefore, you cannot change the "BR Class 156" from Oovee to "Class 156", except by solution B. However, changing the "Class 158 DMU" to "Class 158 (Sprinter)" works in both cases because it has been 'specified'.
Therefore, if you try to change the name of the "BR Class 156", it will simply disappear from the menu, unless you go via Solution B. The same applies elsewhere (e.g. Changing "MKS Class 460" to "Class 460").

To download TS Tools: https://www.railsims.com/TS/ts-tools.php

If you have any queries about this process, feel free to ask in the comments as well. Let me know if this secret was useful.