This is all getting a bit cross-wired.
Yes - RHC have constantly told people not to use power tools for prepping blade surfaces. In any case, any qualified engineer would understand that the immense local heat caused by a power tool on any surface can cause heat damage. Let alone the effect on bonding.
Generalspecific's problem might be related to location. How often does the helicopter get left in extremely strong sunlight with no cooling breezes ? The surface temp of black metal can rocket in those circumstances, causing heat sink back into adjoined components and materials.
I would suggest that a full disclosure of the circumstances to both your RHC distributor and RHC would get their attention. Blades are covered by warranty - so there must be a reason why they feel yours don't get that cover.