Q: Procedure to Change UID in El Capitan

The unique address you're looking for is called a MAC (Media Access Control) address.

Here is a writeup about MAC addresses.

AirPort base stations: How to view WAN and Wi-Fi MAC addresses - Apple Support

Have You tried to create a new user and access the Windows share? If the problem still exists, then it should not be related to the share-client.

However, do you use authentication when you mount the Windows share?

Open System Preferences -> Users & Groups

Click the lock then enter your administrator credentials

Hold the Control key down while clicking on the user you want to change the UID for then Advanced Options

Click the Create New button in the Advanced Options window

You need to be logged into a different account from the one you want to change, if needed, create a temporary admin account.

I apologize, after reading again I see where you want to change User ID instead of UUID.  However, the instructions for that are the same.  User ID is located in Advanced Options of Users & Groups.