So, I understand you want to make your mod a little more personal or unique by changing around the doctrines! Congratulations! Editing doctrines is challenging, but rewarding when you see the results.
What you'll need:
1) Corsix's Mod Studio
3) RGD skills
4) Your new abilities/upgrades
First, I recommend you take out a piece of paper, a pen, and start messing around with layouts in your head. Trust me, this leads to more interesting, unique, creative, and balanced trees. When you have done this, read below.
Ok. I am going to assume you have the mod studio, so open it up when you are ready. First, let's open up the doctrines for your desired race. For example, to edit the American trees, go to:
Ok, open the tree you want to edit. Let's look at the Airborne tree (attrib/attrib/commander_tree/allied_airborne_tree.rgd)
Expand all of the children in the rgd.
Unless you are a genius with programming, there are only a few things you can really mess around with concerning looks and text.
Getting Down and Dirty
There are a few things you can 100% edit in the tree: the name, description, the main images, and upgrades. I recommend you do not mess around with the upgrades, as this can really mess up your mod.
Changing the name is probably the easiest thing to do here. Simply open up name, and insert the UCS reference there. To change the tree description, open up help_text_1 and repeat. Click save. You have now changed the name of your tree and the description!
Now, let's change some pictures. There are a few images you can change. You can change:
These are the 3 I have had the most success with.
Find the original picture in:
Convert the image into dds or tga, and edit it with photoshop or the GIMP. When you have finished, convert the image back into the standard format.
Save, and you have just finished changing the images ingame!
"We Have An Upgrade!"
I bet you are thinking, "ok, I don't really care about the images right now. I want my abilities ingame!"
Remember what you need to have: patience.
Now here comes the fun part.
If you have already drawn a layout of your doctrine, I applaud you. The rest of you, do it now. I'll wait. No, seriously, go ahead.
With the knowledge of your tree nearby, start making your abilities. If you need help with this, ask around on the forum.
When you have all of your abilities ready to go, go to the requirements for the ability. Here's the fun part.
Have the abilities require the upgrade for each part of the command tree depending on its position. For example, upgrade\allied_airborne_02.lua is the 2nd ability on the right side of the tree. By doing this, whenever you get that upgrade, you have access to the ability!
After you have done all of this, try it in game. Save everything, and try it out.
Wait a minute...why don't my new abilities work? That, my friend, is because there is one last step to do.
Putting It All Together
Lastly, we need to have all of the abilities show up on the command panel before we can use them! This is probably the easiest step of all.
Simply go to attrib/attrib/racebps/(race)
In your race, find abilities.
Yep, you guessed it. These are the doctrinal abilities that show up on the command panel.
Simply replace the old ones with your new ones. Save, and try it again.
Well, it is true that you learn something every day. For example, you read this, and now you know how to edit command trees. I wish you luck with all of your modding endeavors and congratulate you once again for being a modder.
Kapp EDIT: For further reading on editing doctrines, please see Aidas' How To here