My question involves a child custody case from the State of: California

So my husband has primary custody with the mother getting the 1st, 3rd and 5th weekend along with half of summer and half of holidays. The ex is wanting full custody and has even told my step son that she will file for full custody once my step son turns 12 years old. She believes that at 12 years old my step son will be able to chose whom he wants to live with. I know that he can't because he's not 18 but his wishes are included in the decision. There is no abuse. The main problem that step son has with us is that we don't let him do what he wants (hours on end of TV and video games, chores, homework) and he says he wants to get to know his mom and play with his brother. To me this doesn't seem like reasons to transfer custody over. His mom came back into the picture almost 4 years ago, so him wanting to get to know his mom seems weird to me.
Either way, the mom and dad live in different but neighboring counties. In the court order, it states that we can only live in those counties without any permission from the other parent. My husband and I are in the process of buying a short sale house in the county that she lives in. My step sons birthday is in August.
If, let's say, the court date is after we move into the other county, can we ask for a change of venue AFTER she files?