This is a basic one but I encountered this and was wondering how it makes sense.
\begin{align} 2x + 3y & = 9 &&\text{Rearrange into the form y=mx+c :} \tag 1\\ 3y & = 9 - 2x && \text{} \tag 2\\ y & = \frac{9}{3} -\frac{2}{3}x & && \text{} y & = \frac{-2}{3}x + 3 && \text{} \tag 1\\ \end{align}
Yes as long as while shifting we move along with the sign It is allowed .
Subtraction is not Commutative for example $a-b$ can not ne rearranged to $b-a$ but it can surely be written like $-b+a$ if we move the signs along.