We have some unusual length fasteners that have been custom made by our fastener supplier. for example in the AS standard, M12 x 75mm long, which are not present in the standards on the toolbox. Is it possible to add custom length fasteners into the toolbox? I know it's not ideal to have lengths outside the norms, but we have a large amount of historical designs that I have to deal with.
You cannot add to the out of the box Toolbox standards, but you can copy one of the standards and add additional sizes to your copied standard.
http://help.solidworks.com/2010/english/SolidWorks/toolbox/allcontent/solidworks/noncore/toolbox/t_copying_standards.html?format=P