Question

It's adj.for sb to do sth 中的sb可否换为doing sth

Answer 1

不可以的.

It's adj.for sb to do sth

for sb to do sth是真正的主语,sb是to do sth的逻辑主语的.

如：

It is impossible for him to get up early.

It's important (for me) to carry on practicing speaking for learning English.

本句中的practicing是on的宾语；speaking是practicing的宾语；而learning English是for的宾语；for learning English是状语.