I'm not sure about tools specifically for your first question, but as for your second question, yes, definitely!
Decompilation is useful for understanding code, but it is terrible for modifying code. Compilation and decompilation are both lossy processes. Also, there's a lot of things you can do in bytecode that have no Java equivalent, so you shouldn't ...
The encryption key is stored in the variable f4800b. It comes out to the following byte array.
43, 57, 97, -68, -63, -61, -40, 9, 50, 87, -104, 101, 63, 34, -78, 60
The cipher algorithm used is Triple-DES in ECB mode. It can be decrypted by the following snippet. Note that it requires the BouncyCastle Crypto provider for Java.