On Install, legacy sites will not be effected at all.
They will only be effected if you make edits to them using Data Bridge.
Right now, there is a known bug with editing the insert and update behaviors from data assist 2, but we will be releasing an update soon to correct that problem.
it is always a good idea to make a backup of your site before making any changes.
You can always set up a new user on your computer, and under that user install the standalone extensions, use that user for making edits and use your current user for any new sites you create