I’m not sure about Graphene specifically, but as long as there’s an established procedure documented, I’ve done like fifty installs of custom Recovery and various ROMs, such as Lineage, crDroid, Resurrection, Havoc, Cyanogen, AOSP, AOKP, ASPCA [:-)], WKRP [:-)], etc. and dozens of other less well-known ones, and I have not bricked one yet. So, as long as you don’t do anything blatantly foolish, should be ok.