Magnetization orientation in Ga+-irradiated Pt/Co(d(Co))/Pt ultrathin films can be changed in a controlled way by adjusting the ion fluence, F. Two-dimensional (d(Co), F) diagrams of magnetic and magneto-optical properties have been derived. Distinct out-of-plane magnetic anisotropy states with enhanced magneto-optical effects were evidenced for specific (d(Co), F) values. This rich behavior originates from two competing mechanisms: intermixing of Co and Pt atoms at the interfaces and the formation of ordered CoPt alloy phases with high magnetic anisotropy. The irradiation-induced effects open novel routes for both tailoring thin-film magnetic and magneto-optical properties and patterning of magnetic nanostructures.