An would that box be an IBM i or another type of server?
its attached to an ibm box
I think they are saying the linux box will become unstable.
Dunno who 'they' are but it sound a tad 'un-linuxy' (is that a word?) for your box to just go unstable by changing a password. Then again, it's not an IBM i...
Obviously, if you'd have e.g. FTP traffic between the linux box and the i and you change the password used there, this FTP communication would end. But that has nothing to do with the stability of the box.
Reckon you have to go find yourself a more Linux oriented forum to get the final answer to your valid and relevant question.