You are essentially just changing the translation value so the only implication is if you change the actual meaning. For example, if you changed Required to be Optional, all existing selections that were once "required" will now be "optional". I'm not sure if your example is changing the meaning or if you are just being more explicit. Another option would be to archive the previous value and create a new one. Then you can handle any migration issues manually or using a db script.
I believe the character limit is 150.
Hope this helps,