Hi Cecile,
How are you planning to create vendor master data? I believe you have also posted for mass creation of vendor master data without using LSMW. There are two options you can go for:
1) If creating LSMW then you can change the code for making default values for few fields. Let me know if you are taking this approach and then I will tell you in detail or ask your ABAP consultant to help you with this.
2) I already suggested you to create mass upload program for this if you don't want to use LSMW. It can be easily done by using BADI (VENDOR_ADD_DATA) or BAPI (BAPI_VENDOR_CREATE) and then you can ask ABAP consultant to provide default values for certain fields. That can be even conditional for example for certain company code you can default values for payment terms or payment method.
Let me know how you are planning to create vendor master records
Regards
Pankaj Pareek