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Don't do it that way. Instead, type into the project field in the row, and you get the benefit of the quick match feature as well as not having completed projects shown. If you don't have the project field shown, you can add it with the gear menu at the top of the outline's scroll bar, or with View→Columns→Project.

To me, the inspector is the means to set any field that can be set to (nearly) any allowable value (the exception that comes to mind is that you can't set project or context to a value that hasn't yet been defined).