You can unassign using delete pay item data then all or as the data is attached as Xdata you could try express tools can't remember if there's anything in there.
Otherwise a lsp routine to remove all Xdata or .net tool to do the same will work.
Mike Evans
Civil3D 2022 English
Windows 7 Professional 64-bit
Intel(R) Core(TM) i7-3820 CPU @ 3.60GHz (8 CPUs), ~4.0GHz With 32768MB RAM, AMD FirePro V4900, Dedicated Memory: 984 MB, Shared Memory: 814 MB