I noted that expansions for Z3TA+ 2 such as for example Cakewalk Mutant Reload are not listed in Command Center. I forgot how I installed them on my old computer. Do I just download them? Thank you.

Yes, download the installer from https://www.cakewalk.com/My-Account/Products and run it.

Never mind, found it. Thanks.
1) Unzip Dark N Dirty - 2.0 version.zip to C:\Cakewalk Content\Z3TA+ 2\Programs. To do this, right-click Dark N Dirty - 2.0 version.zip and select “Extract All”. You will be prompted to select a destination folder.  You can copy and paste C:\Cakewalk Content\Z3TA+ 2\Programs into this field. You can also click [Browse]. In the “Select a destination” dialog click Computer and then navigate to C:\Cakewalk Content\Z3TA+ 2\Programs. When the location is correct, click [OK] and then click [Extract].
2) Open Z3TA+ 2 and select “Dark N Dirty” from the Bank menu at the top of the user interface. Choose a category, select a patch, and enjoy!

My mistake, I thought they were installers. I just check one of the Mutant series, they are zips with instructions in rtf format. It has been a while since I installed z3ta+2 expansions.