Modifying your hardware always renders warranty worthless. For simple reasons. If you did something to the hardware, it's no longer possible to say that the fault is a birth defect, or if you introduced it. After you did anything, your relying on goodwill gestures from the manufacturer rather then warranty.
Hence, adding a fan that blows over the Indivision by means of sticking it to the RF shielding is OK, where as bolting it on a ACA630 cooler, is a different thing entirely. Jens also explains exactly how the cooler is supposed to work, and at what temperatures it's expected to keep the hardware, explaining that there is no need, what so ever, for a fan on the ACA630.
Heck, in exact opposite to what is stated in that thread, many GFX brands for the PC market will void your warranty if you as much as take the shroud of a factory cooling unit, and clean it, to then reassemble it again. Allowing you to replace your cooling with a better one, or just taking it of to replace the heat transfer paste, is a complete no go for 95% of all brands, with the exception of the enthusiast lineups, where they charge you enough to afford user introduced faults as a part of warranty claims.
Not sure what your gripes about warranty is, really.