if I am on an M-1 visa I will not be able to change once I am in the USA
Yes you will be abe to change on an M-1 visa.
You actually have 6 months to do so.
The caveat is that the school needs to amicably agree, they are obliged to transfer you in the SEVIS system.
Most do some don't. Get in writing beforehand that they will transfer you if you are not satisfied.