Updated: May 10, 2020
Any mantra can be written by all. Writing this way is called as Likita Japam. If you write it in left hand (non-dominant hand) it is even more powerful.
How the purpose behind writing a mantra is served? A mantra can be used for several reasons. Write the mantra as many times as you can. The mantra knows the intention behind your writing. So, the purpose behind it will be achieved.
If you keep chanting all these mantras, say for an hour, they will be chanted automatically in the head without your effort. They are so powerful that they will be heard automatically inside the head.