[ShadowChemosh]

The sClass.? tag is on the spell itself NOT the class. The spells say I belong to X class via a tag called Spell Class (sClass.?).

In example if you wanted to add Cure Light Wounds to the Wizard/Sorcerer you would start by adding CLW to a cleric. Right click on the ? to get the unique id. If this does not work go to Develop->Enable Data File Debugging.

Next in the editor go to the *Extend Thing tab and click new (blank). Then enter the CLW spell ID for the "Thing Unique ID". The the "Group ID" is "sClass" and the "Tag ID" is the class tag (ie cHelpWiz) for wizard and cHelpSorc (for sorcerer).

Save and use CTRL-R to restart HL. Nothing here requires you to copy and make a new version of a base class. Actually that would be harder to do and make lots of future issues.