Be aware that adding additional masters to your mod will re-number the formIDs of your own items (as your mod will no longer be the 2nd in the list (01), it will be the 3rd or 4th depending on how many DLCs you use.
I ran into this when I wanted to Remove some masters from my mod, and it caused me some trouble. I recommend using Fo3Edit to add the additional masters, as Fo3Edit will re-number the formID dependencies so that everything lines up correctly. Adding masters is very easy in Fo3Edit, and you get the extra checking and numbering to boot.
Luck!
Miax