No it will not void warranty. It's upto you to contact customer care or not. If you getting support from them then it's best way to ask them to do for you
Very simpleDownload samfw tool (for pc) from said website and connect device to PC and follow on screen instruction for change csc. It's 2 min procedureAnd you don't needs to flash Indian firmware because you're already have milticsc firmware install...
You're having multi csc firmware and simply changing csc to INS will make your device exactly like you bought in IndiaVisit samfw.com and change csc to INS (it's free service)
