I was facing some issues with the character's encoding. Those are resolved by updating the CHARACTER and COLLATE for some columns in the table. So my concern is if this conversion is safe? Or does this can create issues for different encoding techniques? Also how to convert the CHARACTER and COLLATE for multiple columns of the table in the same MySQL query?
There are many possible impacts. First, what command did you use to change the charset and collation?
The "correct" way is to
ALTER TABLE .. CONVERT TO ...
Any other change is likely to have messed up the data. To check for that, please provide
SELECT col, HEX(col) FROM .. WHERE .. for some non-English cell in the table.
If you have "garbage" coming out of your app, see https://stackoverflow.com/questions/38363566/trouble-with-utf8-characters-what-i-see-is-not-what-i-stored for further clues.