I have try it my development server, and it's work
actually, this question for my requirement that need do integrate between another system to CRM, which the another system has guid as their PK (primary key) and they push their record to CRM using CRM web service and put their PK / guid value as Id in CRM's
entity that they pushed.
but, I have consult with microsoft support with this technique and I don't want get trouble in later time, and they said this is not recommended from microsoft, even it work as I said before.
thanks.