My ex has custody but my sons been living wth me for almost two years, can I get temporary custody?

My ex has custody and my son has been living with me 75% of the time and going to school by my house for almost two years. Now she wants him back and wants to enroll him in school by her house before the end of the school year even. He is 10 and wants to live with me. Can I file temporary custody and have him stay until I take her to court for custody? She even has filled out and signed school papers stating his residence is my address. Can I get a temp order and do I have a chance of winning?