I'm also searching for how to block a value of MD5. Still didn't found the solution friend. If you found the solution friend guide me also to it.
It depends what products you're using. VSE does not support blocking via MD5. HIPS supports blocking of program execution via MD5 as well as all version of ENS. I believe ENS 10.5.3 will support blocking all file types by MD5 via expert rules.
If you're using tie you can change the reputation of the file to known malicious if it's an executable.