Student192:
Changing the pen set, so that pens are changed globally, can lead to unexpected results, as you don't know how the pens are used in every element in the project. Also, you would need to check the default settings for every Object, Door and Window, and each one can have many pen settings.
In your example, if you have 30 walls to alter, you can view all walls in the 3D Window (if the walls are on multiple floors, otherwise you can use the 2D Window), open the
Find & Select... palette, and you will able to add Criteria(s) so only the walls you want to alter are selected. This is a very powerful tool for making selections. Once a wall has the correct settings, you can alt/option click on that element to make it the default settings for that tool.
Thanks for adding the signature.
David