In Modern Standard Arabic, the word may change slightly if you make it a gender specific. Let me demonstrate this in the following points:

• If you were addressing a man, you would say: الله يحفظك (ِAllah Yeḥfaẓak).
• If you were talking to a group of men, you would say: الله يحفظكم (Allah Yeḥfaẓkum).
• If you were addressing a woman, you would say: الله يحفظك (Allah Yeḥfaẓek).
• If you were talking to a group of women, you would say: الله يحفظكن (Allah Yeḥfaẓakunna)
• If you want to apply gender neuter, you can simply say: الله الحافظ (English: God bless) (Allah Al Ḥafiẓ)