How to retain security role using Plugin on change of BU?

Dear Experts,

We got a requirement where we want to retain security roles of users when the BU of that user is changed to another BU.

We have tried it through PreOperation but couldnt get the solution.

My doubt is when we changed the BU then its security roles will automatically get removed then how we can get the existing selected roles for existing BU.

Can this be achieved by plugin or is there another way to retain these security roles?

Please let me know the solution.

Thanks in advance