When you're worried about your ex-spouse overstepping and hurting your relationship with your child, it makes you frustrated. You hate that you'll punish your child and not be able to get support. You don't like that they make it out like you're being uncaring or unfair.
A situation like this can be harmful to your child, so it's important that you speak up if you're having issues with the way your ex-spouse is parenting or getting involved in your parenting. You should both be on the same page when it comes to caring for your child, so if you can't agree, that's a big problem.
When conflicts happen often, it may be a good idea to go through mediation to address your parenting agreement. If you can't get your ex-spouse to do so, then you may want to take them back to court. If they're undermining your relationship with your child or negatively impacting your child's life, then you should make it clear that you need that to stop.
If a parent isn't a good role model, can you fight to take away custody?
A judge may be willing to change your custody agreement if the other parent is unreasonable or is dangerous to your child. However, mere differences in how you approach raising your child aren't likely to be enough to result in modifications in custody.
If you are sincerely worried about the situation your child is in with the other parent, talk to an attorney. They will be able to get to know the situation and determine if it's worth trying to go to court for a modification.