>How can I know if an INDEX TAG exists?. I want to delete an especific index tag (if it exists, of course) before create a new one.
>
You can use TAGNO() function

IF TAGNO("myindtag") > 0
  * Tag 'myindtag' exists
ENDIF

However it's not good idea to delete and recreate individual indexes because it causes index bloat and slows down data access. Maybe there's another way? Why do you need to delete and recreate an index?