It seems that the answer to my question required both of your answers(@MC ND and @Ekkehard.Horner); also, once I changed the vbs script to open and write to the .rc file in Unicode, which I'm not sure why I have to, the script was able to execute without error.
Here is the vbs script in it's final form:
Const ForReading = 1, ForWriting = 2
Const TristateUseDefault = -2, TristateTrue = -1, TristateFalse = 0
Const DoNotCreate = false
rcFile = "C:\Path\To\RC\File.rc"
major = 4
minor = 3
maint = 2
build = 1
version = major & "," & minor & "," & maint & "," & build
Set fso = CreateObject("Scripting.FileSystemObject")
Set fileObj = fso.OpenTextFile(rcFile, ForReading, DoNotCreate, TristateTrue)
rcText = fileObj.ReadAll
fileObj.Close
Set regex = New RegExp
regex.Global = True
regex.Pattern = "(PRODUCTVERSION|FILEVERSION) \d+,\d+,\d+,\d+"
rcText = regex.Replace(rcText, "$1 " & version)
regex.Pattern = "(""(ProductVersion|FileVersion)"",) ""\d+, \d+, \d+, \d+"""
rcText = regex.Replace(rcText, "$1 """ & Replace(version, ",", ", ") & """")
Set fileObj = fso.GetFile(rcFile)
Set textStream = fileObj.OpenAsTextStream(ForWriting, TristateTrue)
textStream.Write rcText
textStream.Close
The only thing that does not seem to work is the regex for replacing the ProduceVersion|FileVersion values, but hopefully I can hammer that out within a reasonable time.