I have put some data together and modelled the behaviour of the response ($y$) as function of three independent variables $x_1$, $x_2$ and $x_3$. A simple multi-linear regression. The model looks like:
$y = k + a*x_1 + b*x_2 + c*x_3 + e$
Up to this point everything is OK. But now I want to lower the response by a $15%$. Like reducing some commissions or costs. The only idea I came across is to multiply the responses by $0.85$ and readjust the whole model. Recalculate $a$, $b$ and $c$ with the new values. I have been trying to find another way of doing this without touching the data samples. Just changing and adjusting the coefficients $a$, $b$ and $c$. Does anybody know how this should be done? An idea you come across with would be okay.