解: (1) 根据题意,得$\begin{cases}2a+b-3=-2,\\-a+2b-3=4\end{cases}$
解得$\begin{cases}a=-1,\\b=3\end{cases}$
$∴x※y=-x+3y-3,$
$∴3※(-6)=-3+3×(-6)-3=-24$
(2) $∵\begin{cases}(4m-2)※(2m+3)>6,\\(2m+3)※(4m-2)<6\end{cases}$
$∴\begin{cases}-(4m-2)+3(2m+3)-3>6①,\\-(2m+3)+3(4m-2)-3<6②\end{cases}$
由①,得$m>-1,$
由②,得$m<1.8,$
$∴-1<m<1.8,$
$∴$整数$m$的值为0,1