Of course. The only real requirement is that the person making the will be competent to make the change. In the movies, you have probably heard this stated as “being of sound mind”.
A will can be modified with an addendum, often referred to as a codicil or replaced by a completely new will.
Sometimes the law can modify the effect of a will. This is especially common in cases of divorce which usually terminates an ex-spouse’s rights unless a specific provision keeps them in place. However, separation doesn’t terminate a spouse’s rights.
This just one example, but a probate attorney should always be up to date on prevailing legal issues in your state.