Hello, I`m starting to learn how to create new objects and I want to create a bigger arch, one that overseizes the one with de width of a door. How do I edit the functions of the original arch to cut the walls inside the perimeter of the new one (a 3 doors seized for example)

I`m from Argentina, I hope you understand my english :P

The "hole" in the wall is obtained by adding properly named TXTMs (the so-called "wallmasks") to the package. Each tile need to have 2 wallmasks (a "north" and a "south" one).
You can check the "Hey Nonny No Arch" that came with the University in order to see how a multi-tile wallmask works (that door is 3 tile wide and 2 tile high).

I actually suggest you to start your new object by cloning that arch (remember to check the "Create Stand Alone" and the "Pull Wallmasks" options).

Next, you have to delete the Object Data that refer to the upper part (the OBJD to delete are the ones whose name ends with "1"); delete also the Object Functions and the Name Reference having the very same instance numbers than the deleted Object Data.

Now, just edit the mesh as usual (remember that the original mesh is 2 tiles high!) and texture it.

Thanks Numenor, I haven`t seen you answered my question till today. THX, you`re a great helper.
Za