A court can basically do whatever it wants if it believes it is in the best interest of the child. But I don't think that's the question you really want answered.
The first thing to check is what your divorce decree says. If it grants you certain
visitation rights, you ex can not take them away from you. If she tries, file fore her to be found in contempt of court.
But it sounds like the situation is even simpler than that. You have a
court order which defines visitation. Ex is trying to change that. In order to do that, she's going to need to prove to the court that it is in the children's best interest to spend less time with their father. THat is going to be pretty hard to establish.
In your shoes, I would consider a counter suit (since she has filed to adjust visitation). Father would argue that since Mother is now living only 45 minutes away that even more visitation is warranted. It would not be at all disruptive for the kids to spend a lot more time with their father. Ask for every weekend and one night a week during the school year and every other week during the summer. There are plenty of research studies that establish that when kids spend lots of time with both parents they are far better off - so you could offer that as justification (studies are available on this site).
You might not win, but I would bet that the most likely outcome would be for the existing court order to be reaffirmed without change.
Although this one shouldn't be that complicated, your odds of favorable outcome probably improve if you can get an attorney to handle it. He/she would be familiar with the case law in your state and might know how the judge is likely to respond to any given argument.