Hi Boomerang,
Best to speak to willem or Pierre at Raasa... but yes you will definately need to redo your ATF in the new partnerships name. Just as you will have to re register it in the partnerships name at CAA. You will also have to tfr your radio licence to the new partnership as well...or get the new partner to apply for his own.
We went through this process in November when Stef and I bought TC's old plane DBP
Step 1: CAA registration (At CAA)
Step 2: AP Inspection and new ATF (at RAASA)
Step 3: Radio Licence Tfr or application.
BUT:....here's something everybody needs to take note of:
An ATF is only valid if it is the same name as the registered owner/s of the aircraft. To effect a transfer of ownership, you need to fill in the CAR47A form (avalable from the CAA website). The current ATF will be
invalid from the time both parties sign the form and fill in the
date of transfer... Thus it will render the ferry flight (if any) as an illegal flight

My advice is to "post date" that section of the form by a few days so that you can at least have time to ferry flight on the current ATF.
That is as I understand it to be....perhaps Willem or Pierre can clarify it better.