The affix ṭhak comes in the sense of 'appointed there' after a word in the Locative -7th case (tatra) in construction.,
Thus शुल्कशालायां नियुक्तः = शौल्कशालिकः 'a superintendent of custom-house.' So also आकरिकः, आपणिकः, गौलूमिकः, दौवारिकः ॥ The word तत्रनियुक्त is a Tatpurusha compound formed by 2.1.46. The word niyukta here has a different meaning from that in 4.1.60, hence its repetition here.,