This new feature is announced and explained in detail in their recent blog post entitled, "New Feature: Do-it-Yourself Historical Record Fixes." This feature on MyHeritage.com is not only intended to "fix" transcription or indexing errors but also to correct information contained in the original document such as clerical errors on the part of the person who wrote the original record.
This concept moves the process of indexing into a closer association with those who are doing research in original documents. In the past and as is also the case presently, indexing projects are conducted either by paid contractors or volunteers. The marvelous work done by these indexers has revolutionized genealogical research. But very very few of these contractors and volunteers are experienced genealogical researchers themselves. Adding a feature, such as the one introduced by MyHeritage.com, allows those who are actually involved in the research process to increase the reliability of the existing indexes.
Obviously, the original record is not altered. The fix involves adding alternative readings of the record. What is most helpful is that MyHeritage.com automatically adds the alternatives to their search engine technology, SuperSearch™.
Rather than reproduce the entire blog post, I suggest you read the original article linked above.