when you said that your nurse license has been pre-evaluated, what was the SCH verdict? anyway, whatever if SCH's determination of your license it will be stored in their database. So if you change your agency, all the documents you will submit will have to be sent to the concerned govt. entities in Qatar. Your license will again be sent to SCH (by your 2nd agency) and SCH will of course find in their database that your license had been evaluated and has been cleared. I guess that's is and you will have no problem at all