IS THERE THE WAY TO CHANGE "PASSAGE" OPTIONS FOR EACH TILE ON THE MAP SPECIFICLY?

Firstly, you could probably just look this information up in the help file (or, there's this handy hover-help feature in Ace where if you hover over a command a small pop-up with information appears.)

That said:
Passage options are set via the Tileset Tab in the database. I think of you want to adjust them on the fly (like during play) you'd need a script or use events instead. (Or tile change/substitution of some kind.)

For a full run-down check this post.

Regions can be used for many things, but most people use them for defining what monster groups go where on a map. So say you had a world map, you could make certain enemies turn up only in one area, while have others turn up in another. Or make one area where certain monsters appear more often - the weight affects how often out of the groups that particular monster group appears, so you could have a place where an ultra rare monster appears all the time or 1/10th of the time or even make it so that it appears only on one tile, 100% of the time.

They can also be used to reference where the hero or event is on a map. So if you had a rock/button puzzle where you want to define that x amount of rocks have been moved to x spots, you can make a region on each spot you want the rocks and then have a parallel process run to check if those rock events are on that region.

I've used them to define where treasure chests are by having a parallel process check the hero position and see if they are standing on a certain region. If so, and they're also turned a certain direction and press the confirmation command, they find an item. It helps when you're using Lite, that's for sure.

Really, it's all about how you can figure out how to use them. They're pretty flexible.

author=Zachary_Braun
Whenever I've needed to change tile passability on the fly, I make a copy (or more) of the tileset entry in the database, using the same tileset graphic, and then change the passabilities I need to. This makes it easy to switch back and forth.

This is overkill unless you need to change directional passability. It also doesn't work when you have two spots on the same map with the same tile and want only one to be passable. And it probably results in hundreds of identical tilesets...

A simpler way IMO is to make the tile passable on the tileset, and put an invisible event over it when you want it to be impassable.

If you do want to change directional passability, you'll probably need multiple copies of the tile on the same tileset. If you have 16 desks on the same tileset, you can give each one a different passability.