Because of how many comments I'm getting everyday and being unable to respond to each and every one of them, if you're having issues with this method, just add me on discord and I can help you there a lot easier than I can with YouTube comments.
Edit: Since there seems to be some confusion in the comments, make sure you do a hard save on the game before you start. Import [game name].dsv file. The DSV file can be found in the Battery folder that comes with DeSmuMe. After you do all of your edits on PokeGen, save the file in the battery file as [game name].sav. Then, open up your game on DeSmuMe, click Import Battery File, and find the [game name].sav file that you just created, click ok.
BE ABSOLUTELY SURE TO SAVE STATE BEFORE TRYING THIS. If you screw it up and your save gets deleted, you can just reload the save state and try again. This way, you won't lose your save file.
There aren't that many ways to evolve trade evolution Pokemon on DS emulators, and the ways where you can do a legitimate trade are quite complicated and time-consuming. So, I thought I'd share a fairly simple edit. To clarify, THIS IS NOT AN ACTUAL TRADE. But, it yields the same results, as shown by stat increases.
You'll need PokeGen, a DeSmuMe emulator, and a Pokemon rom. You'll have to find links to these on your own. You can get PokeGen here: http://archive.pokedit.com/download/pokegen.php I will not be giving links to roms, so you're on your own for that.
This method will work for any Generation 4 or 5 DS Pokemon game. (Diamond, Pearl, Platinum, Heart Gold, Soul Silver, Black, White, Black 2, White 2).
Follow the instructions in the videos and you will have your trade evolution. Also works for Pokemon that evolve by trading items. It's ultimately your decision if you would like to discard the item after you evolve since you aren't technically trading here, just editing the evolution. If your Pokemon normally learns a move after evolving, you'll have to edit that in yourself.
And yes, evolving it this way will also register the Pokemon in your Pokedex.
* If you get an error such as this, don't panic, just click OK.
Your SAV file should still have saved. This usually occurs if it is your first time editing the DSV file. The next time you do it, the error should not occur. Just import the SAV file and you should be fine. Be sure to do an in-game save after you're finished.
Here's a list of all the Pokemon that should evolve through this method. Ignore the Gen 6 Pokemon as this method is for Gen 4/5.
And yes, technically, you don't need the trade evolution item to evolve those Pokemon. However, I like to evolve the Pokemon once I get legitimate access to the item, and then dump the item afterward. But, that's how I'd handle that. You're free to handle it however you wish.