Sentence:  ... as these passions and principles are inalterable, it may be thought, that our conduct, which depends on them, must be so too, and that 'twou'd be in vain, either for moralists or politicians, to <WSD>tamper</WSD> with us, or attempt to change the usual course of our actions, with a view to public interest. 
Meaning of the word marked with <WSD> tags:  To try to influence someone, usually in an illegal or devious way; to try to deal ("with" someone).