Goto transaction code SU10

Select your SAP User by Address data or Authorization data.

With the users you want to change selected, click :-

User -> Change -> Profiles

Filled in the Profiles and click save.

How can I create multiple User Id at Random

We usually created Id though SU01, it only one by one.
Can I create multiple user id having same profile at once.

Yes you can, use tcode SCAT. First, make sure your client setting (SCC4) is enabled with ' X eCATT and CATT allowed'. Just in case your Production disabled this.

- Then, you need to create a simulation (test case) of creating new user id by calling tcode 
  SU01 later. 
- Test case must start with Z, example ZCREATE_NEW_USER. Create this case, put title and 
   choose component as BC (basis components). 
- Save and choose Local if you dont want to transport it or choose a dev. class (example ZDEV) 
   if you want to transport it later.
- Go back and click Change button. Then key -in Object as example SU01, and choose Record 
   button on top. When it prompts to enter Transaction code, key in SU01 (if for roles, 
   key-in PFCG) and begin recording. As usual in SU01 create 1 user id, dept field, password,
   roles, group and so on. 
- Make sure you press Enter on each field because we want to capture the value/object and 
   SCAT is a bit stupid if you become familiar later....but still useful...indeed. 
- You will see a clock on the bottom which means the recording process is on going. 
   Once done, click Back button and press End button to end the recording.

Note -  I noticed you said the profiles are all the same. Then this is much easier...no need to enter the roles/profiles, just duplicate this ID and change the name, dept and password only.

Okay..first stage has finished. Then double click the Object to begin inserting parameters. Then you will see an object for each fields that you run from SU01. Choose the right field example user id (BNAME) and choose button 'Insert Import Parameter (F6)' and you may click Next Screen to 'watch' what have been recorded and proceed to choose several other objects like password field (PASSWORD1, PASSWORD2), roles field (AGR_NAME), group field etc. If you happen to choose the wrong object, then you can reset back (Edit -> Reset Parameterization). You may see so many junk fields captured and this is because SCAT records every steps/dialogs. 

Once done, choose Back and save this case. Then you need to click 'Goto -> Variant -> Export' and save it. After that use Ms Excel to open it and begin inserting all other user ids. Save and close. Remember to close this file because SCAT will use it.

Then last one, get back to SCAT and click button execute, processing mode chose Background, choose external file 'the one you created with Excel' and execute. At this moment don't use tcode SU01 bcoz you may interrupt the simulation. Wait for the logs.  If you see reds then error was 
happening. 

Hoping this will help you. I have done (Sap 4.6C) this to create thousands of user ids and also thousands of roles/profiles (pfcg). I heard with Sap 4.7, the SCAT has so many extra features.....

Correct me if i'm wrong elsewhere.....just shared my experience.

Related:

• Changing the default password for sap* user
• Function and Role of User Types and DDIC User

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SAP BC Tips - Basis Components

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