Hi Albert
You can create a custom template for the Product Detail and find the line:
@HttpUtility.JavaScriptStringEncode(Html.LocalizeString(Global.LocalizedStrings.Message_ProductNotAvailable, Global.FilePaths.LocalSharedResourceFile))"
and replace with this to print the message returned:
" + data.responseJSON.Message
Then you can edit the static localization for the ValidationResult.resx file for the 3.Text entry.
In the next release, we'll include the line changes available out of the box.