Stata 15 help for _rename
[D] _rename -- Rename variable
_rename old_varname new_varname
_rename changes the name of an existing variable old_varname to
new_varname; the contents of the variable are unchanged. Use [D] rename
in preference to _rename.
As of Stata 12, code form rename was changed to ado/Mata from internal C.
_rename is the old, built-in rename command. It is used in testing
Stata, and when you set version less than 12, _rename is the rename