PlaserBoard Repair

I was hoping somone can tell me how to fix this problem
Near the base of my shower there is a water leak that has rotted the skirting Board and the base of the plaser near the Skirting Board. i would like to know how to fix the Plaster without Re- plastering that whole wall. Can i cut the plaser say 200 mm up from the floor and install a new section ? and if so how do i make the Joint look like its one section as well as making it last without cracking along the joint 2 or 3 years down the track
Thank you

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