How to show specific rows within an unlimited field group?
Yes you can do it by form_alter. Seeing through the code of other similar question, I see that unsetting the Add More button can do it for. You can review that code &amp; apply for your case.

You can do it by help of Field Validation module too, which has been mentioned in 2nd answer &amp; more feasible way. I have also used it for some projects of mine, where I did set minimum &amp; maximum required for a field accepting multiple values.