Ok, to edit the income and move units you have the Edit function. Start a game, and go to the Game tab and select Enable Edit Move. That allows to change the IPCs owned for each country and to add/remove units from territories. When you’re done, disable the Edit mode before continuing with the game or TripleA might crash.
To edit the unit abilities, you need to edit the specific .xml file. Go to the Triplea folder and open the Games folder. You better make a backup copy of the game you wish to edit.
Right click on the .xml file and select Open with Notepad (or an .xml editor if you have one). Scroll down until you find the lines that start with <production>, that will allow you to change IPC costs for each unit.
Scroll down more until you find <attatchmentlist>. After the countries there will be a list of the available units for that game and their properties (attack, defense, movement and other specific ones). Keep in mind that all properties follow Revised rules, i.e., you can’t add things like paratroopers and so on.</attatchmentlist></production>