x <- "(pop+corn+unicorn)-bread+salt+malt"
gsub("\\+(?=[^()]*\\))", "|", x, perl=TRUE)
gsub("(?:\\G(?!^)|\\()[^()]*?\\K\\+", "|", x, perl=TRUE)
eCA8LSAiKHBvcCtjb3JuK3VuaWNvcm4pLWJyZWFkK3NhbHQrbWFsdCIKZ3N1YigiXFwrKD89W14oKV0qXFwpKSIsICJ8IiwgeCwgcGVybD1UUlVFKQpnc3ViKCIoPzpcXEcoPyFeKXxcXCgpW14oKV0qP1xcS1xcKyIsICJ8IiwgeCwgcGVybD1UUlVFKQ==