Can you reverse hairline lowering?

Reversing hairline lowering is very difficult, if not impossible. There will most likely be scars and other undesirable cosmetic changes. This is why I commonly tell patients that I simply will not take the hairline beyond a certain point, and frequently turn away patients that may have unrealistic expectations or desire unnatural results. Removing 2 inches of forehead is an extremely dramatic change, and reversing that amount would be extremely difficult. 2 centimeters is a much more common amount of hairline lowering and might be easier to reverse.

In general, you cannot reverse a surgery.  The only way may be to incorporate tissue expanders but that would take several weeks or months of slowly expanding your skin.

Tissue expanders should be used to stretch the forehead first.  You will have very little change with a coronal incision as another surgeon suggested, after having had a hairline lowering procedure.  There would be increased risk to this procedure due to blood supply issues if it didn't also include the old scar in the excision, and I am not sure if that is what the other surgeon is trying to say.  Either way, the only reliable way to help you is with tissue expanders.

As others have mentioned, tissue expanders can be used, but it is still possible to elevate the forehead and hairline without doing that -- you just might not be able to get a full 1.5 of 2 inches of movement like you mentioned in the question.  The way to do this is simply to excise a strip of the hear bearing scalp behind the current hairline, undermine into the forehead, release the brow attachments, and then elevate the forehead / hairline.  What I just described is a coronal browlift.  The only difference is that the incision placement would likely need to be different than the standard incision pattern based on the location of your previous hairline lowering incision and scar.

Reversing low hairline? Yes this can be done with tissue expansion but would require wearing a scarf to cover your forehead while expanding for 8-10 weeks. 

The size of your forehead can  be increased but this would require placement of an expander under the forehead skin so it can be stretched and permit hairline elevation. I have done this in motivated patients.

The only way I could think about reversing a hairline lowering surgery is with the use of balloon expanders, which would stretch your forehead over a period of weeks.