SDTM Terminology Fixed.xml file

I am fairly new to OpenCDISC and I have been reading the website and have alot of questions about how to do a few things. I need to suppress alot of the errors that keep popping up for extensible codelists where the values are ok, but aren't apart of the software. I am wondering if you can add informations to the file name SDTM Terminology Fixed.xml in order to help with the issue stated above, or is there another way to do this? 

Also, do you have to add user-defined domains to the configuration files in order to get them validated??

Lastly, how do you add user-defined checks to the software?

Thanks!

Paul