Yes, you can ask for new terms using the above link.
If you use the extended term already now, you should add it to the “CodeList” in your define.xml with the attribute def:ExtendedValue=“Yes” (see Define-XML specification).
This won’t make the CT2002 warning go away, as the Validator seems not to do a lookup in the define.xml for extensions to codelists (it should).
Your comment is not relevant to the original question.
A purpose of CTxxxx checks is to report any non-standard terms in submission data. It works as expected. There are other checks which ensure correct implementation of study metadata.
When validating, I get CT2002 “Variable value not found in extensible codelist” for a questionnaire I have used in previous studies and which I am planning to use in future studies. I cannot find a corresponding QSCAT variable value in the CT so I am looking to have it added. I believe the correct way to add a new term to the CDISC controlled terminology would be to make a request through the NCI at https://ncitermform.nci.nih.gov/ncitermform/. Could you please confirm?