In the highly strained system Fe/W(001) the formation of parallel dislocation bundles upon nucleation of fifth layer islands is used to locally break the fourfold symmetry. The uniaxial strain relief in the dislocation bundles introduces strong uniaxial in-plane magnetic anisotropies. By controlling the density of fifth layer islands local magnetic anisotropies are structured on the nanometer scale. As a result of this patterning of anisotropies, the magnetic properties of the films are drastically altered. As a function of the pattern size, the coercivity of the films can be varied in a controlled way over more than two orders of magnitude without changing the film thickness. For pattern sizes larger than the estimated domain wall width, MOKE and micromagnetic calculations indicate the break-up of the film into magnetic in-plane structures on the 100 nm scale.