Is there any drawback in altering an existing column datatype from TEXT to VARCHAR(n)?
The only risk is truncation of data.

Effectively the ALTER will


Create a new table with VARCHAR instead of TEXT.
Copy all the rows over.
Rename to put the new table in place of the original.


So, the question is, will copying a TEXT into a VARCHAR of the same CHARACTER SET do any harm?  The only possible thing is truncation.