Will the XPS 17 be able to accept an Intel Core Ultra 7 155H as an upgrade?

The processor is soldered on motherboard and can not be replaced.  Any CPU/GPU upgrade has to be a complete system board replacement.

Beyond being soldered in, and taking note of the excellent response above, that's a 14th gen CPU -- there isn't going to be a 14th gen XPS 17 model (that's going away in favor of a 16" XPS), so a mainboard swap won't be possible, either.