My assumption is, you have used custom DB function to concatenate two fields in RD. If this is the case, execute the RD from designer studio and find for which value you custom function mapped to, you can verify it "pyMapping" page list under "pyReportContentPage" clipboard page.
Once you identified the mapping, the same property can be used to store in the clipboard.
Suppose that we have mapped pyTextValue(1) to the drop down and later the report definition is modified and one more column is included above the current column which also makes use of some text function then the pyTextValue(1) would be pointing to this newly added column. I was wondering if there is any better approach?