Well most folks aren't modifying the PSU just replacing it. Not that it really matters as the warranty is still valid.
Meridian can only refuse a warranty claim if they can demonstrate that the cause of the claim was due to any modifications or alterations made. If the cause was not due to any modifications or alterations made the warranty is still valid for that claim.

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