What operating system do you use?
You need to recompile you operating system to change character limit for account name.
As I know for FreeBSD files you need to edit are:
Code:
/usr/src/sys/sys/param.h (change MAXLOGNAME to fit your needs)
/usr/src/include/utmp.h (set UT_NAMESIZE to the value of the above MAXLOGNAME + 1)
Than rebuild world (dont know if kernel recompile is needed).