Changing time zone against TOS or not???

Nothing specifically citing fiddling with phone settings. Just the general "People are creative. Don't cheat. We may or may not do something if you do."

They barely take action against spoofers. I doubt they would ban people for timezone manipulation.

Timezone Manipulation is impossible to detect, so banning people that way is not possible. It's the same thing with finding pokemon with scanners or checking ivs with external apps, as long as they don't need your account you can technically get away with it.

By using this trick, I've confirmed that it is possible to get a soft ban. If you switch a day ahead, and then switch back immediately after, the client and server get confused what day it is. Then you can't spin stops for some reason.

I heard of this on Zapdos day. Changing to a certain time zone could give you another 5 raid passes. It seems an exploit of a weakness in the system, and usually is regarded as cheating.

I've been doing it for months now with no ill effects. I think it's technically possible to get a soft-ban from it but it's highly infrequent.

Regarding the TOS, I think there's a clause in there about 'falsifying location'. Obviously a more egregious breach of this condition is spoofing, and is probably what they're primarily referring to, but changing the time zone could be interpreted as a less-severe version of faking where you are for an in-game advantage.

That said, I don't see why they can't force all events to be on server-side local time as opposed to client-side so that this exploit doesn't exist, if they really cared about it.