No warranty issues if you fit lowering links provided that they don't interfere with chassis or moving parts, personally I can't certify this or that lowering link but you should be ok.

A few people have had issues with chain tensioning, but we believe this is probably down to worn sprockets / chain.

Look there is another way around lowering your seating position and that is by having a bike seat upholsterer unstaple the saddle vinyl cover and cut off 2 or 3 inches from the foam in the middle of the saddle where you park yo'ass, and then restaple. It's the best way because not only it doesn't affect the bike geometry but also does away with lowering links and issues with chain tension.

I have had it done to my bike too.