In MySQL, how to manually edit values of a BLOB column in few tuples?
When deciding to store the field as BLOB or TEXT, this paragraph might be helpful:

BLOB values are treated as binary strings (byte strings). They have no character set, and sorting and comparison are based on the numeric values of the bytes in column values. TEXT values are treated as nonbinary strings (character strings). They have a character set, and values are sorted and compared based on the collation of the character set. [src]

The difference outlined here being in the way values are compared and sorted.
You can use the UPDATE statement to modify the values.
Now, from some of the comments, I garnered that this field is a primary key. If this table is InnoDB, and this table has secondary indexes (other indexes that are not primary key), and you expect the table to become very large, then be aware how InnoDB handles secondary indexes.
InnoDB will store the primary key along with the value of the secondary indexes, so your index will grow much larger than if you used an autoincremented int column as the primary key.