Like you posted, this cannot be done.
What exactly do you want to accomplish by doing that?
Maybe we can figure out a way to get to the needed end result by other means.
Hi I developed a Database for my office, its a simple solution with very sensible information. This database needs to be access by 50 different employees. do to security risks I decided no to use one database and give individual password to them. It was best to give separated databases to each one of the. So every time I make an upgrade I have to change the datasource of 50 files manually.
It was best to give separated databases to each one of them.
Well, I must politely disagree with that design decision and the problems that you now have is just one of the major reasons not to make that choice. You can use Manage | Security to limit each user's access to different records in the same table of records. There's no real need to split up the data into all of these independent files just to manage secure access to the data.
See "Editing record access privileges" in FileMaker Help and check out this particular sub section: "Entering a formula for limiting access on a record-by-record basis" for a description of how to set this up.
At first it was like that, but its slow ;(
It shouldn't be slow if you are using indexed fields for this.
Trying to keep and sync multiple copies of the same file up to date is a real nightmare best avoided if at all possible.