Conjugate[expr]

Questions
1

I was wondering is there a way to replace complex I to -I. All variables in the expression are real, so basically i just need that switch of I.

2

How about

{a + I b, c - I b, d + I (e/f), g + I (h^i)} /. Complex[0, 1] -> Complex[0, -1]

(*Answer: {a - I b, -I b + c, d - (I e)/f, g - I h^i}*)
3

Thanks!

4

ComplexExpand[Conjugate[{a + I b, c - I b, d + I (e/f), g + I (h^i)}]]

This is more reliable in terms of how it will handle numbers such as 4+5*I. You might want to wrap inside Simplify[...,Assumptions->h>0].

5

For long expressions, it takes too long.