Here's the repo for the Namecoin fork of Armory:
https://github.com/namecoin/BitcoinArmory. If you are checking out the commit history, make sure you look as far back as this commit:
https://github.com/namecoin/BitcoinArmory/commit/90351e11601cc5e2c09481dad6b56f6a7a4f620e.
As you can see it hasn't been updated since late 2014. For now, it is abandoned. You can see some reasoning in the
remaining open issue. That issue also links to
this thread of which you are also the original poster, so you are probably already aware of that thread.
The necessary changes were already covered well by knightdk. For Namecoin, we still needed to touch the C++ code even though Namecoin uses the same hash algorithm as Bitcoin, because we needed to use a different directory to load blocks from (~/.bitcoin versus ~/.namecoin on Linux) and because Namecoin uses merged mining, so the block parsing needs to account for that. For Litecoin you definitely need to touch the C++ code to use scrypt as the hashing algorithm (as knightdk already stated).
If you don't know where to start, the Namecoin fork is better to use as a reference than nothing, even though it is outdated.
