Can you fancast voices for characters?

Because if Ducktales dived into Mrs. Beakley and Webby’s backstories (sounds like Season 2 and up material), I want the voice of Webby’s mother and Mrs. Beakley’s daughter to be voiced by either Hayley Atwell (1) or Billie Piper (2). Just cast any kickass British ladies.

FOOTNOTES:

(1) Going by her roles as Peggy Carter in MCU films and other Marvel Properities including her voicework in Avengers: Secret Wars and her role as Cinderella’s mother in 2015′s Cinderella.

(2) Least likely candidate. I have to admit, it’s based off of David Tennant and Catherine Tate’s roles in Ducktales and I just want Billie Piper to be included.