After closing outlook app, new defined bullet (character code 45) gets deleted from bullet library

Hello,

I have been using the special dash character (code 45) for constructing my body text but, to use this character I have to go to Message tab then Bullets -> Define new bullet... In the pop-up window, I select the character (code 45) and I am able to use that. This character becomes part of Bullet Library. As long as I keep the outlook app open, I am able to use this character quickly using Bullet Library but, when I close the outlook app it disappears from Bullet Library. 

I like to keep this new defined character part of Bullet Library even after closing the app. Could someone point out how would I do that?