# [Japt], 10 bytes

    r"%d*$" +V

[Try it online!][TIO-j3lrkje5]

     r"%d*$" +V
    Ur"%d*$" +V # Implicit input (U and V)
     r          # Remove
      "%d*$"    #   any trailing digits
    U           #   from the first input
             +V # And append the second input
                # Implicit output

[Japt]: https://github.com/ETHproductions/japt
[TIO-j3lrkje5]: https://tio.run/##y0osKPn/v0hJNUVLRUlBO@z/f6XEpGQlHQUlE1MzJQA "Japt – Try It Online"