Hey Guys, Thank you very muchfor the advice.

I will try to use SQL functionality in a test environment first, Thanks a lot

Below is a C# code to add one DNN role ("Role1") to every DNN user in DNN portal (Portal id = 1)

//create role controller
DotNetNuke.Security.Roles.RoleController roleController = new DotNetNuke.Security.Roles.RoleController();
                
//1. Get DNN role                
DotNetNuke.Security.Roles.RoleInfo role = roleController.GetRoleByName(1, "Role1");
                
//Gets all the users from the portal id =1
System.Collections.ArrayList dnnUsers = DotNetNuke.Entities.Users.UserController.GetUsers(1);

//for every user
for (int i = 0; i < dnnUsers.Count; i++)                
//add role 
roleController.AddUserRole(1, (dnnUsers[i] as DotNetNuke.Entities.Users.UserInfo).UserID, role.RoleID, DotNetNuke.Common.Utilities.Null.NullDate);