Right now creating some optional integrations between assets requires manually defining scripting symbols. This can be automated with scripts but creates multiple problems, one of them being that these symbols don't get automatically removed when the asset is no longer on the project. A solution for this would be adding support on UdonSharp for version defines, these are already recommended by vrchat as a way of detecting the VRChat SDK (https://creators.vrchat.com/sdk/detecting-vrcsdk/) so it makes sense that its supported for custom packages too.
This was also already implemented on Merlin's version of UdonSharp so it should be an easy addition: https://github.com/MerlinVR/UdonSharp/commit/0e3ab4c4858af0bd6ec071a8e9a2cefa39428ce5