I didn't say it would be easy but it is the law and since it has precedent most certainly isn't an assumption.
Changing the PSU is a modification to the unit but not to the PSU, either way it's a semantic argument and doesn't affect the legal position on the warranty.

Sources: MS600, Fidelity Audio Reference Oppo UHD-203, Roon/QNAP, AppleTV 4K
Processors: Arcam AV40, 271 x2, Lumagen 5348 with Keces P8
Speakers: DSP7200SE FL/FR, DSP5200SE VC, DSP3200 x11, DSP320.2 VOG, DSW x4
Display: JVC DLA-N7 with PK-EM2, Panamorph Phoenix Pro, 128" 2.37 Curved Silver Ticket AT Screen