xps laptop hardware differences between windows and linux

As ejn63 says, in theory they could require that.  But I'll say this.  I've worked in various IT roles over the last 15 years or so, including in roles where I was responsible for supporting hundreds of laptops, including dealing with warranty repairs when needed.  So I've dealt with far more warranty claims than the average person.  And I never ONCE was required to return my system to its factory state before I could get warranty service.  Especially in this case where Dell themselves sell and therefore support this system model running both Windows and Linux, it just doesn't make sense to me that they would refuse to support you until you installed the original OS that your particular system shipped with.  If you were buying a system that Dell only sold with Windows and tried to call about Linux issues, then yes that could definitely be a problem.  But this isn't that situation.  You're actually thinking about starting with Linux and moving to the much more COMMON platform of Windows.  I just can't imagine that being a problem.

I agree with ejn63 that if you want to play it safe, then ordering the laptop with the OS you plan to run is the safest approach.  But if that would be significantly more expensive because you'd be paying for a license that you didn't need since you had access to some other licensing source, then if I were in your position, I wouldn't hesitate to buy a Linux configuration.  And while I of course can't know for sure or make any guarantees, I would be stunned if Dell wouldn't support my system while it was running Windows.  If anything, that would probably make it EASIER, simply because Dell sells vastly more Windows systems than Linux systems and therefore they will have more support staff that are set up to provide Windows support.