One question regarding this matter of TO's and walls: is there any possible way to enter a region guarded by a garrison and start a TO (avoiding to engage in combat with the defenders), in order to refrain them from using the walls?
No. If you do not control the battlefield, you cannot start a takeover.
(That actually may not be not strictly true, as there may be some odd edge cases involving having a third party present to confuse the troops into not fighting...but any deliberate use of such tactics would be considered abusive, and I'm hoping to be able to do away with them soon anyway.)
