Time to wipe the dust off this one.
I found myself in a similar situation as the OP where I want to exclude code using Conditional Disable Structures.
In my project, I have multiple Build Specs and I wanted to change the Conditional Symbols based on which Build Spec I'm running. For example, I could have a Debug and Release Spec.
I know that the IfDef.llb (LV\resource\plugins\Utility\) provides a SetSymbols.vi, so my first thought was to have a Pre-Build Action which calls SetSymbols.vi to set my key-value pair. That works fine.
This could turn messy if there are multiple Symbols that might need setting for different Build Specs and instead of having lots of small vis that each set a single Symbol I want something a bit more manageable. So why not allow setting of the Symbols via the Build specification description?
So I made a small vi that you can drop in your Pre-Build Action.vi, which reads this text and sets any of the symbols it finds.
LcExtra_IfDefSetSymbols.viLcExtra_IfDefPreBuildDropIn.vi
People who don't like this idea may want to replace reading the Build specification description with reading a separate .txt file which they include in the project that contains symbols for all possible build specs. There are many ways ...
Of course, if you're in any way interested in this topic, the first thing you should do is support this idea in the LabVIEW Idea Exchange, which would make all of the above obsolete.