Emerging quantum information technologies require robust and tunable single-photon sources in precise locations. Solid-state single photon emitters (SPEs) hosted by mid-bandgap defects in 2D material hexagonal boron nitride (hBN) are bright and stable at room temperature and demonstrate a wide range of strain tunability. While recent studies have narrowed the range of possible defect candidates by demonstrating the role of carbon in hBN SPEs, the methods to engineer carbon-based defects in hBN either produce randomly located emitters or require bottom-up crystal growth on structured substrates. We achieve patterned arrays of SPEs via focused ion beam (FIB) milling followed by chemical vapor deposition (CVD) of nanocrystalline graphite source for carbon diffusion, and find that both techniques are necessary for significant and repeatable creation of SPEs. Furthermore, we leverage the SPE arrays and the rich parameter space of FIB and CVD techniques to elucidate the material and process conditions most desirable for hBN SPE engineering, providing important insights into hBN defect formation. Our technique utilizing relatively accessible materials and resources simplifies the patterning of extrinsic defect-based SPEs in hBN and similarly structured solid-state SPE sources for devices such as photonic circuits and quantum transducers.