Hi Cecile,
Perhaps SHD0 would be useful to create the default values in master data.
Goto SHD0 and enter the relevant Transaction code,(enter FK01 for instance) and a transaction Variant(say ZFK01). Click on Create Button which will take you to the creation of vendor master.
Now if you want to make account group as default Value enter the value and press enter now a screen will pop in that select the account group field and option(with content,output only,invisible or required) and then enter. It will next take you to different sections of master data which ever the field you want to default enter the values and enter
Once all the details are completed. Then hit the "Exit and Save" button, and hit the "Save" button . You will be asked to assign a development package to your transport this can be provided by your Basis team.
When you hit the Back button to go back to the “Transaction and Screen Variants” screen, go to the “Standard Variants” tab and enter the transaction variant in the 'Name' field.
You can then activate the Transaction variant by clicking on the Activate button .
The next time you create a vendor using transaction FK01, the default values will be in the master data..
Thanks,