We review results of magnetooptical studies related to various methods of "spin splitting engineering" possible in quantum well (QW) structures made of II-VI diluted magnetic semiconductors (DMS). The experiments made use of unique structures, based on Cd1-x-yMnxMgyTe, with a precise in-plane profiling of either QW width or n-type doping intensity and of structures with digital profiling of the composition of constituent materials in the growth direction. The most typical version of the spin splitting engineering, available also in bulk DMSs, namely the one via an adjustment of (homogeneous) Mn composition, or via the lattice temperature or/and a magnetic field, was used to study magnetooptical properties of QW containing electrons as a function of their g-factor (tuned from g(ett)* = -1.46 + 55!). We also demonstrate three further methods of modifying the spin splitting in low-dimensional structures made of DMSs. They involve: (i) atomically precise control over Mn ion spatial distribution in the growth direction, (ii) reduction of the s-d exchange constant with increasing electron confinement, (iii) modification of MII spin temperature by the electron gas heated by photo-excited carriers.