1) To alter the overworld sprites, you need Poketex and the HGSS offset .txt file. Poketex is found in the R&D forum sticky. Google to find the .txt.
Put the .txt file in the same folder as the program and rename it "list.txt". Open the rom in the program. Check YouTube for in-depth tutorials. You'll have the option of making a modified Dragonair OW sprite or just using the same one over Dragonite. One other thing: it only works with the Japanese rom for HGSS, so you could use a file system program (look below) to extract the edited a/0/8/1 and reinsert it into an English version rom of your choice. Or not, if you like playing the Japanese version.
2) To alter the stats, you need PPRE. Found in the R&D forum.
Hit "Choose Rom," pick your file, hit "Set Rom," wait, hit "Pokemon," and then just go down the list to Dragonite. Change what you want and hit "Save." Close that window and hit "Write Rom" or "Create Patch," depending on what you want to do. Of course, before you use PPRE, make sure to run the latest Rudolph Child's Play patch on the rom if you're going to use a USA or EU rom.
3) To alter the battle sprites & the party/box icons, you need PokeDSPic & NitroExplorer2, CrystalTile2, or any other file system program. I think they're in the R&D forum, but if not, they're on page 1 of any search engine.
Use the file system program of your choice to extract a/0/0/4 and rename it "4.narc". Open PokeDSPic, select the narc, scroll to Dragonair's first back sprite entry and hit "Save PNG". Do the same with the first front sprite. Open the PNG in Paint or Photoshop, make any edits you might desire for your Dragonair "evolution," and save the PNG (skip this if the regular sprite is fine). Repeat for the the other image. In PokeDSPic, go to Dragonite's first Back sprite entry and hit "Open PNG". Hit "File," then "Write to narc". Repeat for the front sprite. Make sure you replace all 4 of Dragonite's sprites in this way: 2 back, 2 front. Use the File system program to reinsert 4.narc into a/0/0/4. Do it the same way for the paty/box icons using the appropriate program that comes in the zip file. Those are located at a/0/2/0.
4) And although I haven't tried it (yet), I think PPTXT is the only program that can change a Pokemon's name. R&D forum, page 1.