We have studied the effects of irradiation with He⁺ at 80 keV on the properties of YBa₂Cu₃O_7-x (YBCO) grain boundary Josephson junctions (GBJs) and superconducting quantum interference devices (SQUIDs) made on bicrystalline substrates. He⁺ irradiation produces a shift in the position of the Fiske and flux-flow resonances and consequently changes of the Swihart velocity and the ratio between the dielectric constant and the barrier thickness. Interestingly I_C of GBJs can be raised over 10% of its value by irradiation. The modification of the barrier properties depends on the dose and on the particular distribution of the current inside the barrier. By selecting the appropriate doses from the detailed analysis of the shape of the critical current versus magnetic field curve, irradiation offers the possibility to induce a posteriori controlled variations in the properties of YBCO GBJs. These variations imply a decrease in the critical temperature of the electrodes. At this stage of our study, this is the most important inconvenience in using helium irradiation for applications related with nitrogen cooled devices based in GBJs. However, as an interesting example from a scientific point of view, we show the evolution by irradiation of dc SQUID voltage modulation curves, the shape of which are altered by the presence of Fiske steps.