Thank you for writing to JustAnswer Health with your question. It sounds like you must be having some difficulty with pain control.
Typically it is not a good idea to cut up a Fentanyl patch. The reason is, is that the medication is fixed into a membrane and meant to release gradually over time.
As whether you can take hydrocodone while on fentanyl it really depends individually on your case. Ideally you would have one doctor that was following you for your pain control, and then who could decide whether or not you should use an opiate pain pill (such as hydrocodone) for break through pain while you are on a fentanyl patch. There are times when this is appropriate for severe pain, but this depends on many factors and we would not be able to evaluate this adequately over the internet alone.
The danger is that although you have cut your fentanyl patch in half, that instead of getting 1/2 of the medication over several days, you could instead get a bolus (a large dose) all at once because you have distrupted the membrane. There are documented cases of people who have dying after scraping off the gel from a fentanyl patch and taking it all at once, rather than using the patch as directed. Although I understand that this is not what you have done, I am still concerned that the fentanyl will not deliver correctly now that it has been disrupted. This is a controlled substance that should only be taken as directed -- it has effects which can be dangerous if used incorrectly. When an opiate medication (such as fentanyl or hydrocodone) level is too high in one's system, it causes the respiratory (breathing) rate to gradually slow down until the individual stops breathing. They do not even know this, because they will feel no pain, and will often go to sleep before they die.
So really, I must suggest you take the fentanyl patch off completely. If you do not have an undamaged one to wear instead, call your doctor and tell him the situation so that he can either prescribe you a new one, or give you another suggestion. Your doctor should really know any way, if the fentanyl patch is not controlling your pain adequately, so that she can decide whether the patch should be increased or whether you should take another medication along with it for break through pain.