Wind of Change

until the end of the day doesn't fit here, blue will clearly be at an advantage, perhaps "until the turn is taken" should be considered here.

I meant until the end of the turn.

And in general, all this is suitable for battles with neutrals, but it wouldn't stop someone from seizing an opponent's towns and using Town Portal to a place out of reach.

Firstly, you described a problem that already depends on Town Portal, and Town Portal does not come as a package with Dimension Door. Town Portal needs to be nerfed in the same way and have a negative effect added.
And secondly, do you believe that a change which significantly affects battles with neutrals will not affect the confrontation with an opponent?