Appointment Letter Clause For Third Party Payroll?

I require the suggestion regarding third party payroll appointments letters. I am working with the consulting firm and have to make the appointment letter for the employees who are on our payroll but working for other company. In that case the appointment letter will be as same as for the employees for my company or it has to mentioned that they are contractors and any contract period. As we have signed the contract with the company for one year. Kindly suggest and provide if have the format as well.

Dear Member,
The Appointment Letter will be same as the personnel deployed under payroll for client establishment/location/s. Bcoz primarily they are your employees. However, in order to identify instantly you can start mentioning some code before their “Employee ID No.”. Moreover, in the Appointment Letter you can mention the location/establishment name. But same need to be change (if the employee is being transferred to other client / location, which generally not happens).
If you have some regional branches, the ID can be generated on basis of State/Region. The ID in r/o direct employee (your staff) may be given as HO-======.
Hope this will serve your purpose. Fellow members can put more light on the matter.