We and many others ( including @Mehmet_Kavuran recently) have been looking for ways to customize portal. Customer self service in B2B scenario was a definite need we had hoped to address with ERPnext. It would appear there is minimal to no usage of portal by the user base as forum questions about portal customization are never answered. Also, documentation is greatly lacking on generators and other portal behavior.
Posting here for potential future ERPnext users to find as had we known before we started we would possibly have chosen a different ERP solution. We are in too deep to change at this time and will have to remain in the 20th century for now in our customer facing abilities.
It is a bit frustrating there isn’t more info on the Portal and to have more choices on how it operates. I would be using it for internal use, to avoid having to make end users login just to see some basic info.
The only workaround I can think of for my issue is to make the naming series very descriptive, include supplier etc.