Unreal HLSL semantics

We have some HLSL shader code that uses the predefined shader semantics TEXCOORDX to map input streams. We now want to support Unreal as rendering back-end and see that they use ATTRIBUTEX semantics instead. Ideally, we would use the same shader code for both rendering back-ends. The question now is whether we can make Unreal conform and change the shader semantics Unreal uses. I could not find where Unreal defines these but maybe some of you have an idea? Any other pointers on how to resolve this without modifying the shader source would also be greatly appreciated.