I obey wizards in proper authority, although I hardly see the relevance. I use the same words everyone else does. Nobody I know has ever objected to the word 'mudblood.'
Well, nobody except George Fairfax, but he is my enemy so you cannot expect me to listen to him!
Yes, there is hardly any point to time travel if you cannot use it to change the future. It's usually the intention. If you were to tell me, for instance, that someone I know will die in a preventable accident, because you read it in a history book, then of course when I return to my own time I might stop it.
You might try that, if you liked. I haven't met with them. I was told at home that children shouldn't even speak to muggles, and so when I first arrived in Preya that made things rather difficult.