Well, yes, but that's more complicated.
You'd need to unpack the Package that has the Resource you're looking for. The Resource Packs can be found in: Sid Meier's Civilization Beyond Earth\Resource
The Textures themselves are in UITextures.fpk,
You need Dragon Unpacker (can be found via google) to actually open and extract that pack.
Then you need this tool to actually unpack the dds-textures:
http://forums.civfanatics.com/showthread.php?t=389316
The actual File will then be called civsymbolscolor.png (I think other formats can be chosen in the unpacker, but this one is fine)
Then you need to get a tool that can actually edit and - more importantly - save these files as dds. The most common are either gimp or Photoshop. (Gimp is Free, Photoshop is not - and you'd need to google for the dds plugin of these programs)
After saving the new dds you'd then need to create a mod, add your dds file to it and set import into vfs = true.
And that's really all you need to do!
...like I said. It's complicated. 8)
I think there are more detailed tutorials for all of these steps in the Mod Section for Civ 5 though, you might want to do some searches there if you really want to go through the process.