You can't be ingame when making changes to your SavedVariables, you have to exit the game and then do it for it to work.
The icons getting blurry has to do with UI Scale, I think. But if you've found that adding .4 to whatever value you have, you atleast have a working workaround.
With some google-fu, you can find some very recent threads about this on WoWInterface. There were some really good posts in a thread about DBM borders suffering from this, I think. I'm not completely sure, I might be mixing my threads up, but I know there was a good discussion about this recently.
EDIT: Good luck! Maybe someone else will swoop in and will be able to help you more. If not, I'll check back tomorrow.