Vale, ahora si lo encontre.

Añadi esto asi:
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. var tmpBBCode = { wysiwyg:0, bbCode:'attachment', htmlOpen:'', htmlClose:'', icon:'', sourceCode:0, attributes:[{ attributeHTML:'', validationPattern:'^\\d+$', required:1 }, { attributeHTML:'', validationPattern:'^(left|right)$', required:0 }] };
extraBBCodes['attachment'] = tmpBBCode; language['attachment.title'] = "mybb.bbcode.attachment.title";
language['attachment.attribute1.promptText'] = "mybb.bbcode.attachment.promptText";
language['attachment.attribute2.promptText'] = "mybb.bbcode.attachment.promptText";
var tmpBBCode = { wysiwyg:0, bbCode:'SPOILER', htmlOpen:'', htmlClose:'', icon:'/jscripts/wysiwyg_themes/default/images/spoiler.png', sourceCode:1, attributes:[{ attributeHTML:'', validationPattern:'^\\d+$', required:0 }] };
extraBBCodes['SPOILER'] = tmpBBCode; sourceCodes['SPOILER'] = 'SPOILER'; language['SPOILER.title'] = "INSERTAR SPOILER";
errorField = false;
// build editor. pass neccessary variables
tinyMCE.init({
// set active view flag (code or wysiwyg) ($editorIsActive) (default:wysiwyg)
editorIsActive : 1,
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Pero no se visualiza,¿Problema de cookies? o algun codigo incorrecto?
Un Saludo y Gracias.