For whatever reason, whenever I run the below macro (as a macro feature running on rebuild) on a mirrored part it changes nothing. It should be deleting and replacing the material property with some text.

Example of a thicknessmaterial would be "0.250-ASTM A36" so Material would read "ASTM A36".

(The custom property thicknessmaterial actually equals the SW Material. We do this to control the color by using the SW material and color is determined by grade and thickness. A future macro feature I want to make is to control the color automatically by cross referencing the sheetmetal thickness and SW Material, but this does explain this problem...)

Function swmRebuild(varApp As Variant, varDoc As Variant, varFeat As Variant) As Variant

    Dim swCustPropMgr As SldWorks.CustomPropertyManager

    Dim App As SldWorks.SldWorks

    Dim Doc As SldWorks.ModelDoc2

    Dim feat As SldWorks.Feature

    Dim FeatData As SldWorks.MacroFeatureData

    Dim Rebuild As Boolean

    Dim val As String

    Dim valout As String

    Dim bool As Boolean

    Dim Position As Long

    Dim Length As Long

    Set App = varApp

    Set Doc = varDoc

    Set feat = varFeat

    Set swCustPropMgr = Doc.Extension.CustomPropertyManager("")

    bool = swCustPropMgr.Get4("ThicknessMaterial", False, val, valout)

    Position = InStr(1, valout, "-")

    Length = Len(valout)

    MsgBox swCustPropMgr.Count

    bool = swCustPropMgr.Delete2("Material")

    If (0 < Position) Then

         Doc.AddCustomInfo2 "Material", swCustomInfoText, Right(valout, Length - Position)

    Else

         Doc.AddCustomInfo2 "Material", swCustomInfoText, valout

     End If

    Set evHdlr = New EventHandler

    Rebuild = True

End Function

I found a way around this by deleting the custom property "Material" out of my part template. But I see this is a dumb work around, and I see other people having problem with mirrored parts custom properties with macros and I am not confident enough to know that I am doing it right.