If you're looking at tuning down a half step...... and your guitar is setup for .10's... I would say just go out and buy a set of .11's. Install them... you shouldn't need to file the nut if you're going up one gauge... But if the strings fit tightly... just take the string and move it back and forth in the nut a little bit. This works for the wound strings... The wound wire acts as a kind of tsudo sandpaper... it will give you the necessary clearance without having to file the slots down... If you have to remove nut material... it should be very minimal. You most likely won't have a problem with the gut strings... After you install them and get them fitting properly... Tune to 1/2 step down... Then play it and see where the trouble spots are. Look for buzz... or high action. Chances are... the action is going to be slightly higher. You can fixe that with a simple turn of the truss rod though. Do a small adjustment... play it to see the effects of the adjustment... Keep doing that until you get it where you need it.

Since you're planning on going from .10s to .11s there shouldn't be a lot of stuff that you need to do... The change between the two isn't significant... and the extra tension of the slightly heavier strings should be counteracted by the fact that you're tuning down a half step.. You might not even have to do any adjusting... it may cancle each other out... haha. good luck.