If you install this over item # 1191177, will you void the warranty?

Hello Matt - thanks for reaching out with your question. No - the SmartCore Soft-n-Sound LVT underlayment is one that is approved and will not void our manufacturers warranty. Please be sure to follow the manufacturers guidelines / instructions when installing both products. (Side note: since the Style Selections Arcadia LVT already comes with a pre-attached underlayment, the use of an additional one is not needed. We would use this type of underlayment if the flooring was being installed on top of a concrete slab - since it's also a vapor barrier.) Hope this helps answer your question. Thank You -