In a closed primary state, not many are going to go through the time & trouble of registering back and forth between primaries and general elections (and it wouldn't be hard to prohibit such behavior if it became a problem). I moved to VA from CA where, thankfully, an open primary concept was rejected by the voters - one thing CA does right.
Here in VA, an open primary greases the skids for nominating someone the majority of Republicans don't want. This to me is just as big an issue and problem and this signature fiasco.
It’s theoretically possible for an organized effort to use a primary (open or closed) to choose a different nominee; many Republicans tried that in several states to vote for Hillary in 2008. Nonetheless, Obama still won. It could happen, but, IMO, it’s very unlikely.