Regarding Custom Spells:
[ul][li]Creating custom spells that are visible clientside is NOT possible without modifying the actual Wow client via MPQ edits.[/li]
[li]If you want to make serverside custom spells (spells which effects wont be visible to any standard client) create an entry in spell_dbc to fit your needs.[/li]
[li]If you want to edit the dbc data of a spell via core look for LoadDbcCorrections in SpellMgr and do your edits there.[/li]
[li]DBC nor client modifications are supported on this forum, so please refrain from asking any questions regarding the two[/li]
[/ul]