generel question about UIDs

[Pumuckl]

Hello,

can I add new users manually or does plesk override the UIDs ?
I know this problem from confixx, but there i can define the range of min. and max UID for confix. How does it work with plesk?
Does plesk override UID which I've added manually?

For example, I've added a user and the UID is 1003, but if I'll add a new user with plesk, what will happen? Will plesk take the next free UID (in this case UID 1004) or will plesk override the UID 1003 ?
If yes, can I set the min and max uid for plesk in a config file like in confixx?

Thanks in advance for your help!