Return on two different ways to construct a portfolio
I'm not sure I follow, but do the two portfolios mean the following? 

For portfolio (1),
$$
r_i - r_f - b(r_m - r_f) = r_i + (b-1) r_f - b r_m
$$
and for portfolios (2)
$$
r_i - b r_m - (1-b) r_f = r_i + (b-1) r_f - b r_m.
$$
So, writing them out like this, they look the same.