Old user removed, now having DEFINER errors
as You can see from text of both commands - they not work with data other than single table, so from this point of view - both safe.

In worst case - You already have not worked views and continue have them :), but it not expected result.

But, in any case - the best practice - make backup before any kind of similar operations, so You always can rollback.

Notice in server documentation:


  The server manipulates the mysql.proc table in response to statements
  that  create, alter, or drop stored routines. It is not supported that
  the  server will notice manual manipulation of this table.


more related to other types of manipulation, like - manual edit of BLOB object with text or parameters, but change definer - it just change single column.