Hi!
Personally I’ve used this method to retrieve the token yesterday, and it worked.
Yes, I’ve download an old version of the app (more instructions on referenced reddit page).
So in my case the old version of Xiaomi Home app was installed on an emulated and rooted Android system, but sharing same Xiaomi-credential as my main phone. Then I did not need to install old version on main phone
However I’m sure that if you install the old version on your phone, it is enough to use it just the time to retrieve and copy the token. After this you could (…and should) install again the latest version: your token will stay unchanged.