Unfortunately, because of the nes and snes's bizzare cartridge, you CANNOT run custom firmware. I am VERY sorry to announce this.
But with this out of the way, LETS GET HACKING!
Nintendo 64:
Buy an EverDrive flashcart with an sd card with your (legally) dumped roms and you've hacked it!
The Gamecube is hard and i am way too lazy to write everything so here is the link!
And Oh, I know the wii cfw INSIDE OUT!
wii:
This console if interrupted might brick the console, so again, BE CAREFUL.
Make sure your wii is on the latest firmware and that it is the original model.
Go to your wii settings and go to internet then console information. That mac address is needed for the next part. Its as useful as mac & cheese. Get it?
Then, go to please.hackmii.com, type in the mac address and cut either wire and save the file. After that, format your SD card to FAT32 and extract the letter bomb files to the SD card.
Eject the SD card SAFELY, put it on your wii and wait for a message to appear in the home menu. Once it appears, click on the letterbomb.
Once it pops up a warning about reselling the software, press 1 once it says: "press 1". I know, I'm smart, am I?
Then once a blue menu appears press A to continue.
Go up to the "install homebrew channel" option and press A. Then, go to "yes, continue" and press A. Once it says its installed, press A.
Go down to bootmii, press A, go up to the option "install bootmii as ios" then press A.
Then, go to "yes, continue" and press A. Once it says its installed, press A.
If you have the option to "Install bootmii as boot2", do the same thing and install it.
Press "Return to main menu" and press "Exit".
You will boot into the Homebrew channel. Go to "exit to system menu" and press A.
It is hacked but it is HIGHLY RECOMMENDED TO BACK UP YOUR NAND.
Then Create an apps folder for homebrew, and a wbfs folder for Wii games!
If you have another model wii, go to this website.
Nintendo switch (2):
WARNING!!
I dont know if this can work on the switch 2, and because of the big modification wall, it might brick it.
Bricking Risks:
We ask that you acknowledge that EVERY time you modify your system, there is always the potential for an UNRECOVERABLE brick. A brick is a damaged device that can no longer function; in other words, something that becomes "as useful as a brick".
Bricks are rare on the Nintendo Switch, but still a possibility — so make sure you read the directions CAREFULLY before performing them, and follow them EXACTLY.
Keep your device plugged in and charged throughout the entire process to avoid data loss or damage from an unexpected power-off.
Because you have to type out your model, you can find the link to that here!