Not exactly, one can always scale or use an existing core to develop an engine for a different role, one example is GE's F101 Engine. Designed solely for the B-1 Lancer, the company later used the core of the engine for their later joint venture engine with SNECMA (now SAFRAN Aircraft Engines) to get the CFM56. Current CFM LEAP also heavily draws on the same core although it's been optimised a lot. And while it's been a while since RR Designed any military engine, they still perform a lot of maintenance and overhaul related activities for those engines as they're also used as Aeroderivative Marine Gas Turbines and as Industrial Gas Turbines, which means the data, the knowhow and the know-why is all there in place.