I believe this to be a bug in 2012-- you can change the bolt set by including both sets in the spec
and then when you CTRL + Left Click the bolt set, you can choose the set of your choice. You will know you're doing it right when you see a yellow triange (as opposed to a cyan triangle) that will allow you to change fasteners.
In my experience, everything changes EXCEPT for the bolt length. This was very frustrating for me, as the bolt length was the only thing that needed to be changed with all my different bolt sets.
So as a workaround, what I've done is type in all the different bolt sizes and lengths in the "Long Description (size)" property in the catalog editor.
Then in properties, I changed the BOM so that the template is "Grouped with independent columns"
Under "fasteners" I unchecked "ND" and instead inserted the "Long Description (size)" column instead. Then over-rode the header so that it still says "ND" just so it matches the other categories.
Its a little crude, but its the only way, at least, for me to not have to go and manually input the bolt different bolt lengths for different situations.
