is their a way to change my custody agreement with my exwife over our daughter so she may move freely move to another state with her

Custody is always modifiable as it is neither you or your ex-wife's right. Rather, it is the child's right under California law.  I am not sure where you are in your paperwork but, depending on that, there may be a way to keep your children here.  You need the advice of a good family law attorney.  I suggest a Certified Family Law Specialist.

It sounds like what she means is that when she marries, her spouse may file for a step-parent adoption and if you approve it, you will be giving up any rights to your child.  If you value your child and want to see her then I would think that you would not approve this. If you wish to allow your ex to move from state  to state with the child, you can file a 'stipulation' that is signed and notarized by both you & your ex, stating that you agree with the child moving from state to state.  However, there should be provisions in there such as specific times that the child will spend with you, no movement out of the country etc.  These should be discussed with an attorney so that you understand your legal rights and what would be reasonable in your circumstance.  An attorney should write the stipulation.