How to update the character table of MAX7456
To solve this problem one would need to get the builtin character updating sketch work (Max456WriteTable.cpp in examples folder). After the sketch has been compiled one would have to connect either FTDI cable or a USBASP programmer to the board and upload the sketch to it.

The character set (array) itself used in the code can be updated with the appropriate program available at this site.

UPDATE: In the end I solved it this way. 

Many thanks to Charlie Hanson &amp; Nick Gammon.