Given language consisting Turing machines is decidable or not?
In other words, $L=\{\langle M \rangle:L(M)\notin \{\phi,\Sigma^*\}\}$. you can show explicit reduction from a language you already know is not in $RE$. for example $\overline{HP}$ (it is a very standard reduction).
or you may use the rice theorem to show that.

I did not understand the reduction you suggested.
The reduction from the language you suggested could be as follows:
$$f(\langle M \rangle,x)=\langle M_x \rangle$$

$M_x$ on input w:


run $M$ on x for |w| steps.
if $M$ accepted then reject, otherwise accept.


Note that $\epsilon \in L(M_x)$ in anycase, so $L(M_x)\neq \phi$. and $L(M_x)\neq\Sigma^{*}\iff x\in L(M)$. the correctness follows.