A kernel driver runs at Ring 0 — the highest privilege level in Windows. A buggy or malicious one can do almost anything: leak data, install a rootkit, even stop the system from booting. People are right to be cautious about any tool that installs one.
HWIDChanger does not ship a kernel driver
HWIDChanger works entirely from user mode, through standard Windows interfaces. It does not install a Ring 0 driver. Its risk profile is that of an ordinary user-mode utility — not of a system-level component.
Why other tools' drivers are a real concern
Some HWID utilities do ship their own kernel drivers, sometimes unsigned or signed with a leaked certificate. Avoid those. Microsoft revokes such certificates regularly, and a revoked or faulty driver can leave a machine in a boot loop. A program from an anonymous forum that wants to install a driver is a serious risk.
The honest trade-off
A user-mode tool cannot reach firmware-level identifiers — SMBIOS, the CPU, the GPU UUID. That is a real limit. But it is a limit we accept on purpose: fewer capabilities at far lower risk beats more capability with a real chance of bricking your system. If you ever do need a kernel-level operation, use only properly signed drivers from a vendor you can verify.