Is a healed sprained knee different than before it was sprained?

Yes. An ankle sprain means that the ligament has torn and healed. Even after the healed scar tissue has matured, it will not be as elastic or as strong as the original.
Yes. Once we experience any lesion in our bodies we will never be the same, but time will let you know. You are probably prone to have another sprain in the future.

Related Questions

My sprained knee never healed. Is it too late to get it fixed?

Depends. It will depend on the grade of injury and the ligaments and tendons involved. "sprains" to the acl rarely get stronger but get less painful where mcl and lcl often get better with conservative treatment.