If someone is on a non-B with work permit and their work is due to end, can they convert the non-B to an Ed visa without leaving the country? The documents for the Ed visa would come from a language school like Walen, not a university.

You can try, but suspect they will send you abroad to get an ED-visa. But a lot might also depend on the contacts the school has with immigration.

Do try, but be prepared for the case they say no.

We have tried many times and this is not possible with for private language schools. One trip to obtain an ED visa will be required. It is a bit of a pain in the neck but not much can be done about it.