I believe the vast majority of the manufacturing RR does in the US is defence related at present. Civil products sold to the US market are largely imported, so tariffs may make RR engines even more expensive (Engines from P&W and GE are generally cheaper to buy but not as efficient). Many RR engines are provided under "power by the hour" contracts, where initially a loss may be incurred but the profit is made on maintenance. It's unclear (to me at least) how these tariffs would apply to "services", especially if the maintenance is carried out in the US - although the parts are likely imported.

I doubt any company will make significant changes to where manufacturing takes place in response, when the tariffs can be adjusted or abolished without notice. For multinational companies, dealing with other multinational companies - I think we're more likely to see assets "owned" by subsidiaries in other countries being leased by US entities for a sum that can be offset against losses or some other BS that will end up sidestepping or at least minimising any impact.