Its available as a frame only, so I was going to suggest that you could build on to your own spec.
However, as is often the case, they’ve made a strange decision by bundling the rigid fork with the frame. By doing this, what should be an empowering option now forces you down a particular route.
They really ought to offer the frame and fork separately, so that customers can do exactly what they want. If I was in your position, I’d find this very frustrating.
Having said all that, Genesis make brilliant steel hardtails so, if you can settle on the choice between the two models you mentioned, you should have a great bike.
My altitude 00 is 8 years old and, in singlespeed configuration, is still providing me with big grins.