So can one buy and use the 140W charger with the 14"?
You have always been able to use higher wattage chargers with Apple devices. Even going back to the original MagSafe, you could use 15" charger (believe ~85W) with the 13" machines (believe shipped with ~60W OEM).
There is a full compatibility list for the 140W charger, which includes many older models that did not require 140W:
Mac Models
MacBook Air (M1, 2020)
MacBook Air (Retina, 13-inch, 2020)
MacBook Air (Retina, 13-inch, 2018 - 2019)
MacBook Pro (14-inch, 2021)
MacBook Pro (16-inch, 2021)
MacBook Pro (13-inch, M1, 2020)
MacBook Pro (13-inch, 2020)
MacBook Pro (13-inch, 2016 - 2019)
MacBook Pro (16-inch, 2019)
MacBook Pro (15-inch, 2016 - 2019)
MacBook (Retina, 12-inch, Early 2015 – 2017)
The 140W USB-C Power Adapter offers fast, efficient charging at home, in the office, or on the go for your 16-inch MacBook Pro (M1, 2021). Buy now.
www.apple.com