Somewhat related to this previous post, is the location of the ACA.dll file. While this has not necessarily moved its location, if you were to copy the ACA.cuix and rename the copy in order to customize the copy while retaining the out-of-the-box version, you will also want to copy the ACA.dll file and rename the copy to match the name of your copied CUIX file, in order that your copied version will maintain the tool icons that are defined in that DLL file, such as ribbon tool icons for the AutoCAD-Architecture®-specific tools.
For the Autodesk Bulding Design Suite Premium 2014 package, the default installation location for the ACA.dll file is the
C:\Program Files\Autodesk\AutoCAD 2014\ACA
folder. For older releases or non-suite versions, you may need to look in the folder in which ACAD.exe is installed. Depending upon how your file permissions are set up, you may need administrative rights to copy/rename files in this folder.
I ran into this today because I wanted to have a separate profile to which I can add my own customizations (additional search paths, additional trusted locations, additional tool palette file locations and partial CUIX files) without messing with the office-standard, along with an associated workspace. Since the workspaces are defined and saved in the CUIX file, I decided to make a copy of the office standard CUIX file under a different name. That will require that I keep my copy of the CUIX coordinated with any changes to the office standard, but it will prevent me from having to strip out my customizations should the need to modify the office-standard CUIX arise in the future.