Re: Present Perfect and Past Simple in one sentence
I usually agree with what probus writes, but unless this is an AmE/BrE difference, I can't support that that "that has changed since" is a better sentence than his original one.
We have mixed tenses in sentences all the time. I didn't like him when I met him 1999, but I have grown to love him sinse. I started working here in 2003 and will celebrate my 10th anniversary in July. And so on.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.