Tools help to get stuff done.
Flash Reverse Engineering
- Bytecode Editors
- Flasm - edit AS2 bytecode
- RABCDAsm - edit AS3 bytecode (can even edit multinames)
- Yogda - edit AS3 bytecode, but good for searching strings and identifying DoABC blocks to edit
- JPEXS Free Flash Decompiler (ffdec, googlecode/asdec) - see deobfuscated AS2/AS3 ActionScript beside bytecodes, can edit
- Sothink SWF Decompiler - view recompiled AS2/AS3 ActionScript, can reassemble .fla and show thumbnails of sprites
- SWFWire Inspector - view recompiled AS2/AS3 ActionScript
- Miscellaneous Tools
- SWiX - Edit some tags (like shapes and text) as XML
- SWFiD - Detect some packers/crypters and dump from memory
* Free software is good.
** Free and open-source software is even better.