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.