Two conditions have to be observed here, before undergoing synthetic hair operation: One is that this must not be used to deceive a prospective husband or the like.

The other is to be aware that the woman’s hair is a part of her `awrah that must be covered by her hijab. Thus, you must not expose your hair except in front of your maharim (unmarriageable male relatives).

It is also noteworthy that if this synthetic hair will be removable, then you will have to remove it when performing wudu` and obligatory ghusl. But if it will be as irremovable as a part of your scalp, then you do not have to remove it in these cases.