Spells in the map editor and the Grail in the Conflux?

As far as I remember, placing the Grail in the Conflux, while a guild of mages is present there, allows you to learn all spells upon subsequent visits, even those forbidden in the map editor. However, you won't be able to learn the spells that are forbidden in that specific Conflux. In case of any doubts, such things should be verified either during map testing or on a separate "test map." And always test maps that you intend to distribute, as maps with errors circulating on the Internet are a bad thing! Always immediately record any errors detected during testing, rather than relying on memory, which can sometimes fail. Also, be sure to fix errors that other players report to you. The excerpt you quoted (it's a pity you didn't add a link to the source) seems to refer to any ordinary town, but not to a Conflux with the Grail. As far as I remember, even if the guild of mages is level 1, the Grail in the Conflux will unlock all spells of all levels.