We need a way to change the identity of a variable, the equivalent of changing a column label in an exchange file. Recently, a dataset was identified where the pH variable can be more specific (from PH to PH_TOT). Ref https://github.com/cchdo/data-issues/issues/1084

This needs some new machinery in hydro that does the following:

• Change the variable name of the primary and any ancillary variables (flags, errors, etc...)
• Updates attached ancillary variables
• Updates/adds/removes the attributes
  • whp name
  • whp unit
  • cf standard name
  • flag definitions
• Optionally sets/resets the print string
• Should not change the flag or data values themselves
• Updates appropriate provenance attributes (tbd what they are)