active directory change question regarding affects on exchange 2013

Good day,

  I have some universal security groups that are meant to be distribution groups in a 2008 R2 active directory forest.  These groups are being utilized by exchange 2013, I plan on turning these groups into global distribution groups in active directory (all changes will be made in active directory only, not in exchange).

  Question is; What will happen to the mail boxes using this group? Will it break the mailbox? How will users be affected?

 I plan on doing testing of my own but if someone else has already done this and has ran into issues this will help me out greatly.