It seems to be possible (I tried for now with Homeworld 1 Classic in 1920x1080 in Win7 64 bits).
Simply follow instructions here :
- for Homeworld (remember to be in "decimal" when you change the value)
- for Homeworld 2 (Edit : I launched the game, it seems that my desktop resolution of 1920x1080 is directly detected, and so available in the resolution options !)
- for Emergence

I have different structure that it is described in manual:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Sierra (not Sierra On-Line) - and nothing inside

Which version of windows do you have ?
(Unfortunately, I'm not sure I'll be able to help :P)

it is Windows 10 Home x64

Well, I don't know Windows 10 at all... May be it's stored somewhere else in the registry ?
Did you tried the (laborious) way of "Ctrl+F" to look for "Homeworld" in your whole registry for exemple ? (hit F3 to see the next result of the search) May be you'll be able to find it this way :)

You might need to launch the game with administrative rights so the according registry keys can be created/read.

However I think this game is one of the few cases where you might be better off using a lower (non-widescreen) resolution because:

1) the hud text and click space scales with your selected resolution, making it somewhat tedious to navigate around in higher resolutions.

2) the view distance is relatively short (for a game that takes place in space) which makes the game feel more empty than it actually is. Increasing the resolution only emphasizes that feeling in my opinion.

2) using non-native resolutions might have some side effects. One that I noticed for sure is that your cursor and the actual position on the movement disk are not aligned anymore which makes move commands on a larger range impossible (it either won't take the command or you'll end up at a slightly different position than you selected).

You're making good points, but it's still nice to be able to have widescreen for people who wants it :)
What would be the ideal resolution for a 1920x1080 screen in your opinion ?

----------------
By the way, for interested people, here are the instructions for Homeworld Emergence, provided by XeidiDent :
1. Go to the game installation folder, right click "cataclysm.exe" then click on "Properties";
2. Click on "Compatibility" tab then check the box "Run this program as an administrator" then "Apply";
3. Run the game and go to "Options" and then "Video". On the left, select "(GL) Default OpenGL" and then select any valid resolution on the right;
4. Close the game and open "regedit";
5. Browse to "HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Sierra On-Line\Cataclysm";
6. Double click the key "screenDepth", select Base "Decimal" then change the value to "32";
7. Double click the key "screenHeight", select Base "Decimal" then change the value to to your screen height (1080, for example);
8. Double click the key "screenWidth", select Base "Decimal" then change the value to to your screen width (1920, for example);
9. Close regedit and play the game.
----------------
Edit1 : Updated the method with another one, shorter and more clear than the previous (that you can find here).
Edit2 : And see for the solution linked by Shukaku in this [url=https://www.gog.com/forum/homeworld_remastered_collection/classic_versions_widescreen/post10]post ;)
And as indicated by tinyE, there should be a "Tools" folder which can help the configuration too.

I just found this :
1) Run Homeworld.exe once as Admin. You don't need to make this setting permanent. So don't make it permanent by changing the program's properties. I tried this and it caused the launcher app to crash when I select HW1 classic later on. Just right click the exe and select Run as Administrator.
2) Select a different resolution from the options screen - just to force the registry entries to be created.
3) Exit Homeworld.
And then, hopefully, you should have the registry entries.

If you go to Tools you can change it to a higher res too. Seems to work fine though I just briefly tested it out on the tutorial.

I wish there was a faster way to do it for the original.

This guide is one I would recommend for HW1 and Cataclysm (HW1 CD copy, Cataclysm either CD or GOG version): http://www.rpgcodex.net/forums/index.php?threads/get-original-homeworld-running-on-a-widescreen-resolution.36682/

If the registry keys do not exist, do not manually create them. Reinstall the game as an admin / make sure UAC is disabled on your system.

Go to your Start Menu.
GOG Games, Homeworld Emergence
There should be a folder there called "Tools".
Click on the nGlide Settings icon in it and the configuration should give you all the options.

Oh, I still haven't installed Emergence ! (that explains a lot ahah XD I was thinking you were talking about HW1 Classic, my mistake !) Thanks for the tip, I'll look there when I'll play it ;)

Only useful if you use the 3DFX OpenGL option and that only supports 16-bit, whereas the default OpenGL of the game supports 32-bit and can go up to 1920x1080. The 3DFX option may not be available to everyone.

Thanks. Knew I was missing something.