You can associate more fingerprints images issued from the same finger to the same user. If you do that, the FAR rate will be lower. Significance of the change of FAR depends on quality of fingerprints taken. If you have fingerprints with lower quality the change will be higher. But if you have fingerprints with quality high enough, you may not even see the change. It also depends on database size. The bigger is the database the bigger change of FAR when more images are used. 

On the other hand, the identification time change will be significant. If you use N images for the same finger, you should expect up to N times the matching time than with single image.

We recommend that you would use only a single image per finger, and that if you need more accuracy try increasing the threshold before you use multiple images per finger. But keep in mind that this will increase FRR.