You dont need to use such tricks (i dont know if this i reliable or maybe changed in future.
I would suggest to use additionalresources instead. Here you dont need to set the files to readonly.
See example:
Here you have an folder Resources inside your projectdir. ALL files in THIS folder does not need the readonly-flag.
Put everything what you did in objects/res/ into this folder.
Then, in your project, you can use
#Region Project Attributes
#ApplicationLabel: B4A Example
#VersionCode: 1
#VersionName:
'SupportedOrientations possible values: unspecified, landscape or portrait.
#SupportedOrientations: unspecified
#CanInstallToExternalStorage: False
#AdditionalRes: ../resources
#End Region
to tell b4a to use this folder as additional resource.
If you show me which files in objects/res/ you change then i can show you how to change it.
No need for
#CustomBuildAction: 1, c:\windows\system32\attrib.exe, +r res\*.* /s
anymore