You can also Copy and Paste Bolt types into the same Sub category, so then in each of the Types you could remove the other you don't need. Rename them to reflect your M5. M4 etc. But it seems like a bit of a long work around. Unless anyone else can shed light, go to your reseller.
I'm not an expert in Toolbox, but you can change the colours of specific Bolt Types as I learnt from the SWW15 - SOLIDWORKS World :: Presentation Archives
You can also Copy and Paste Bolt types into the same Sub category, so then in each of the Types you could remove the other you don't need. Rename them to reflect your M5. M4 etc. But it seems like a bit of a long work around. Unless anyone else can shed light, go to your reseller.