Yep! You can mod pretty much any aspect of Next War and any other mod or part of the game.
I'm not sure your level of expertise in modding Civ IV, but in your Beyond the Sword folder under (usually) C:\Firaxis Games\Sid Meier's Civilization IV lies a Mods folder. There is all the data for currently "installed" mods. All the stuff for Next War is in the Next War folder. I wouldn't recommend directly modding that folder in case you want to reverse your changes, so first I would copy that folder and name it something new (make sure it stays in inside the Mod folder though).
From there, the Assets folder is really the one you're concerned with. Inside there are several folders. Art has the Art and 3d models, etc. Python has the python code to run custom events and rules. Sounds has custom music and sound effects. And finally XML contains all the game stats. That's what you want to mess with.
The Art folder has files telling the game what art files to use for units, leaders, etc. Buildings has all of the rules info for buildings, if they add or remove happiness of health and their special properties. Civilizations has the info for the Civs and Leaders. And then units is what you're interested in, has all the unit info. When you open that look for the unit you want to remove and simple delete all of the data between the two <UnitInfo> tags and you're done. You could also fiddle with the tank's Strength or whatever if you think you want to nerf it instead of remove it.
Hope this helps.
