Get/modify taxonomy term info in node edit form field?
I know I can look up each term in
  hook_field_widget_options_select_form_alter since the tids and term
  names are available in the $element, but I hope there is a solution
  which won't require me to re-load/re-fetch the term from the database
  again.


Unfortunately I think you will have to load them again and do the hook_field_widget_options_select_form_alter. There are a lot of functions to load taxonomy information which might be helpful and some of those probably have caches and were used in building the node form so the cache is already primed. 

Is your concern around performance or code complexity?