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Explanation: Hi Alexandra,
a) I have a feeling that the source text is not written by a native speaker.
b) Manipulate is most usually used in the sense of it to handle, operate, i.e. "bedienen", but it can also sometimes be used in the sense of alteration.
c) The "express authorisation" part is normal in many operations manuals, where the manufacturer provides that guarantees lapse, if the machinery is adapted in any way without his express permission.