We have given, for the first time, physicochemical insight into the electronic structure routes from half-metallic to magnetic semiconducting triazine g-C₄N₃. To this end, three material designs have been proposed using density functional calculations. In one design, this half-metal is first made semiconducting via hydrogenation, then tailored with B and N atomic species, which gives a new prototype of the antiferromagnetic semiconductor monolayer HC₄N₃BN. In the others, it can be rendered spin gapless semiconducting with H and B or C, followed by F or O tailoring, which eventually leads to the two new bipolar ferromagnetic semiconductors HC₄N₃BF and HC₄N₃CO. These monolayers are considered to be novel materials in spintronics.