Will column size change when trying to use single unicode character in place of multiple ASCII characters?
"{br}" currently takes 4 bytes in ascii, latin1, utf8, utf8mb4 and perhaps other CHARACTER SETs.  (The "COLLATION" is irrelevant.)

ⓑ is the 3-byte utf8 encoding (in hex) E2 93 91.  See http://www.fileformat.info/info/unicode/char/24d1/index.htm

The size of the table will not change much.  If those things are all that you have, then each {br} will shrink by 1 byte.

If this is an optimization, it is probably not worth doing.

The field (either TEXT or VARCHAR) must be declared CHARACTER SET utf8 (or utf8mb4).  The client must be using utf8.  You should probably do SET NAMES utf8.

There are obscure advantages to VARCHAR over TEXT.  Note that the VARCHAR(100) can hold 100 characters; with CHARSET utf8, that is up to 300 bytes.  {br} is 4 chars and 4 bytes; ⓑ is 1 char and 3 bytes.  The (100) counts chars; disk space counts bytes.

See the following blog for too much more info:
http://mysql.rjweb.org/doc.php/charcoll