You can, just go through the list and for each mobile that is not found (or listed) just add a script for it. You might get lucky and find them in the spawn package you added (nerun's?) within the mobiles folders, or searching around the site here. For simple stuff like the birds, just take an existing generic bird script, and rename it Crow and another Raven, etc.
Otherwise, you could just go down the list, traveling to each spawner location and removing the entry one by one.
If you used XML spawner, you could use the Spawner gump to help you go to the locations a bit faster.. The Premium Spawner is old, and was left somewhat unfinished long ago and is somewhat unsupported now.
By the way, where did you download your RunUO server package? There has been a few folks lately that have asked for help with their 'RunUO' version with some oddities, and in the end we find out its actually an Orb Server.. and that in itself is an issue, because OrbServer was abandoned quite some time ago now, and is a bit of a mess in itself. If you have an OrbServer, that is your first problem