Setting the default CMD/shell Codepage can be neatly done using the following command:
REG ADD HKCU\Console\%SystemRoot^%_system32_cmd.exe /v CodePage /t REG_DWORD /d 437
This will make the codepage 437 your default, but ONLY in the cmd/shell, meaning the rest of the OS is safe and the boot environment ist untouched.
Instead of always changing the codepage whenever the cmd opens, the cmd will open in the specified codepage from start.
If you wish to edit it manually using regedit.exe, beware that you have to set the codepage value in 'decimal' (use the radio-buttons for selecting decimal or hex input).