If I have an earlier build (mod) and dl and run the latest official version, will it leave my existing coins intact? Stupid question I know but better safe than sorry.
Yes, your coins are stored in the wallet.dat file, which simply stores all of the private keys kept in your Primecoin wallet. These private keys will always stay the same, and updating won't change anything about how the wallet.dat works. And if an update ever does change the wallet.dat format, it will be backwards-compatible. Your existing coins will stay exactly the same.