Dear @Coop,
Welcome back to the Wefugees Community and thank you for reaching out to us.
If you hired a new lawyer for the same case he/she will probably ask for your file and the documents from the old one. You can withdraw the power of attorney at any time. I don't see a reason why the former lawyer will have an interest in checking your data - it will be extra work for him/her. However, giving the mandate to another lawyer does not mean that there are no potential fees with the first lawyer anymore.
I hope this helps and please don't hesitate to get back to us with any further questions.
All the best,
Meike