Can a changeling be same as a Halfling in appearance and would their speed still be 30?

@ChrisPerkinsDnD can a changeling be same as a Halfling in appearance and would their speed still be 30?

— Cocoa Wonderpup (@CocoaWonderPup) August 3, 2018

Changelings can’t alter their size. So a medium changeling can’t impersonate a small halfling.

— Keith Baker (@HellcowKeith) August 3, 2018