I think Steve means locking the camshafts at TDC while replacing the tensioners. You can replace the chain tensioners without removing the engine from the car. See the article at the following link.
Pelican Technical Article: Boxster Camshaft Upgrade / Chain Tensioner Replacement - 986 / 987
You can also replace the variocams and their chain rails with the engine in the car. To replace the main chain rails, however, you must split the case which means the engine comes out.
PS: A Durametic will tell you if your camshaft deviations are out of spec. It will also tell you whether your variocams are functioning properly. It may tell you other things relative to your concerns.
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