Is It Possible to Reverse an Alar Base Reduction after Rhinoplasty?

The answer is yes, but I would recommend waiting at least a year to see if you really want this done. The scarring may ease up and you may not need anything at all. However, if you really want it done, the incisions can be re-opened and skin grafts can be placed to open up the nostrils. Good luck!

Alar base reduction involves removing a wedge or section of skin and soft tissue from some portion of the nostril base. Using techniques such as rearrangement of soft tissue from the surrounding areas or skin/cartilage (composite) grafting, these problems can be improved, but will not prefectly reverse the original procedure.

Not feasible.  The scars are not acceptable and the result is not acceptable.  So in short, no it is not reversible.  What can be done is if the nose, bony part is too wide, that can be narrowed to give the appearance and provide a better proportion.
Hope that helps.

 There are ways to revise the scar, but not to increase the width. There is a way to make it appear larger if the nose is over projected.

There are creative things a rhinoplasty surgeon may consider if alar base reductions lead to an undesirable result. These revisions rarely look great, even in the most experienced hands.
Therefore, before doing alar base reduction, you should consider this move irreversible.

It can be improved to some degree by using local flaps but the results will never be that great. There are very few surgeons who can handle such a challenge. The one that comes to mind is Dr. Kridell in Texas. He has a lot of experience in alar base reduction. The second surgeon will be Dr. Fred Stucker in Louisiana.
Regards

An alar reduction or alar plasty will narrow the base of the nose but will not thin the actual alar rim itself. This is the fleshy skin part of the nostril that cannot be reduced due to risk of scarring. The width of the actual nostrils can be reduced by removing a small portion of skin of the nostrils attached to the floor of the nose.

In order to widen a nose that was excessively narrowed, one can add a composite graft of skin and cartilage to the inside of the nose, where the ala attaches to the face. The added scar in this position is not very noticeable. However, such approach can only add about three millimeters of widening, otherwise the scars may become too obvious.
I would not recommend this surgical intervention for cosmesis, I would only recommend surgery to improve obstructed breathing.

It is not possible to reverse an alar base reduction without adding multiple scars on the alar rim amd having to add some sort of graft.  In general, I would say for a cosmetic rhinoplasty it is not done.

Unfortunately alar base reduction is not reversible. It is possible to perform scar revision procedures to help things look more natural, but it is not possible to replace the skin which was removed during the procedure.