  Utilizing the first-principles density functional theory calculations
together with group theory analyses, we systematically investigate the spin
order-dependent magneto-optical effect (MOE), anomalous Hall effect (AHE), and
anomalous Nernst effect (ANE) in a recently discovered two-dimensional
room-temperature ferromagnet $1T$-CrTe$_2$. We find that the spin prefers an
in-plane direction by the magnetocrystalline anisotropy energy calculations.
The MOE, AHE, and ANE display a period of $2\pi/3$ when the spin rotates within
the atomic plane, and they are forbidden if there exists a mirror plane
perpendicular to the spin direction. By reorienting the spin from in-plane to
out-of-plane direction, the MOE, AHE, and ANE are enhanced by around one order
of magnitude. Moreover, we establish the layer-dependent magnetic properties
for multilayer $1T$-CrTe$_2$ and predict antiferromagnetism and ferromagnetism
for bilayer and trilayer $1T$-CrTe$_2$, respectively. The MOE, AHE, and ANE are
prohibited in antiferromagnetic bilayer $1T$-CrTe$_2$ due to the existence of
the spacetime inversion symmetry, whereas all of them are activated in
ferromagnetic trilayer $1T$-CrTe$_2$ and the MOE is significantly enhanced
compared to monolayer $1T$-CrTe$_2$. Our results show that the magneto-optical
and anomalous transports proprieties of $1T$-CrTe$_2$ can be effectively
modulated by altering spin direction and layer number.
