It is done in lieu of refunds. If the calculations support HCE A receiving an ADP refund of $4,000, but they have not used up their full catch-up limit for the year, the $4,000 is reclasssified as catch-up instead of being distributed to HCE A.
What should NOT be done is reclassifying catch to all the HCEs at the beginning of the test. just because HCE B only deferred $5,000 and is over age 50, and 100% of their deferral would fit within the catch-up limit does NOT mean it should proactively be classified as catch-up to give them an ADP of 0% to help the test at the beginning.
The reclassification to catch-up only only occurs in lieu of refunds.
The ADP test is performed AFTER catch-ups are reclassified due to the 402(g) limit. So the scenario only applies to people who are age 50 or older and deferred less than the 402(g) limit + mac catch-up.
Hope that helps.