Updating existing metadata records to address new use cases is an important role of repositories. If the Update Rule is yes, such updates are allowed. If it is no, they are not. Updates = no is very difficult. Try it as an experiment, but be prepared for low metrics caused by empty fields down the road.
After Red fills the F in the third record (because adjacent fields = No), the Updates rule controls where Green can play in round 2:
If Updates is Yes (default), Green can update F, I, or R in record 2. The A in record 2 cannot be selected because it is adjacent to Green in record 1 and Adjacent Fields is No.
If Updates is No, Green must select A, I, or R in record 3 and record 2 will always be empty and will always contribute four empty fields to the metric.