Does having a forehead lift affect your frowning in any way?

One can still frown, One can still frown after healing for several weeks and healing process proceeds. However there are two types of browlift., open and closed. The open technique uses an incision horizontally near the hairline and the forehead is actually "lifted up" and excess skin is remove. The closed lift is done via fiberoptic small scope, and through small incisions. The "lift" is internal with sutures.
May be weakened. A browlift should smooth the forehead and make the patient appear more relaxed (and not "surprised.) in endoscopic browlifts, where no skin is removed, this is done by changing the balance between the elevator of the brow (frontalis) and depressors of the brow (corrugator, depressor, orbicularis.) this will decrease, but not remove, the ability to knit the brows or scowl as strongly as preop.
Depends on what type. There are a variety of forehead lift techniques. Limited temporal incisions, mid-forehead incisions, endoscopic techniques, and the standard coronal and pretrichal incisions. Some of these can be combined with the transection and removal of the frown muscles (corrugators and procerus). Treatment of the frown muscles is strictly optional. Alternatively, the frown muscles can be treated with botox.
Yes. Forehead lifts can modify the frown muscle or not. A detailed discussion with your surgeon is required to understand the pros and cons of each procedure. Many surgeons use Botox or Dysport to stop frowning.
That depends. There are many techniques that achieve a forehead "lift" or "brow lift". Most of them can also include a weakening or removal of the frown muscles that contribute to wrinkling and creases. You need to clearly clarify your goals with your plastic surgeon and the operation should be customized to achieve those goals. For more information you can visit www.Surgery.Org, or www.Plasticsurgery.Org.