Sorry for my poor wording; you did say in your original post that any value that corresponds to a given color will always change your town hall/station to that color, yes. What I meant is that the value from 0x5C738-0x5C739 might control more than just that, since it also acts as the town ID and is repeated many times throughout the RAM (which means other things might cross-reference it which could potentially cause conflicts). The problem nandu experienced is probably the result of only changing that single instance but not the others. I tried to replicate their problem by changing only the value at 0x5C739, and sure enough, all of my villagers acted like I had asked them to move in from another town, but never spoke to them once they did. This is because the town ID stored in their memory (which allows them to recognize their town of origin) is at odds with the value at 0x5C738-0x5C739, but my mayor's ID is saved in their memory. This causes them to think I invited them from another town.
You also cannot send mail, just as nandu said--you know how you can write letters to residents while in someone else's town, but you can only mail them from their post office? That's what's happening here: the game now thinks any letter you write was composed in a different town. New letters you write after changing the town ID at 0x5C738-0x5C739 must use the new value to determine what town they were composed in. However, the post office must remember your old town ID, and is comparing your newly composed letters against it. Since it no longer matches, you can't send letters anymore. Villagers must also use the old town ID (as opposed to what you modified 0x5C738-0x5C739 to) when they send letters, but they're essentially mailing to the wrong address. It's what would happen if you were allowed to mail letters composed in other towns from your own town--even if it is addressed to a villager that also resides in your town, the origin town's ID means nothing in the context of your own game. Therefore, all letters sent after changing that value get "lost in the mail", so to speak. Changing every instance of the town ID to reflect the changes made to 0x5C738-0x5C739 might rectify the problem (old saved mail and such might act wonky though, since it's not stored in the RAM and thus wouldn't get updated with the new value).
Also, it seems the town and mayor character's IDs are heavily linked to how the game creates pseudorandomness. You know how if it's raining on one day, even if you go forward a day and then time travel back to the day when it was raining, it will still be raining (at least I remember it working that way; forgive me if I've jumped to conclusions based on my faulty memory)? That's because it appears to be calculated based on the town and mayor IDs (or at least they're a factor, the date is probably taken into account too when it comes to determining weather). These IDs don't change, hence why the weather will always be the same on a given day. Here are some screenshots:
In the above screenshot it is July 16th of this year, a day that's always rainy in my town. However, instead of the usual downpour, it was sunny after changing all instances of my town and mayor IDs to those of a friend.
Note the clock in both screenshots. The above screenshot was taken right after injecting a modified RAM dump that reverted the town and mayor IDs back to what they originally were. It instantly began raining after injecting.
