Hi Deepthi,
If my understanding is correct about your requirement, then kindly consider the below mentioned point
1. Use GET_I Method of your address field(I stands for input readiness)
2. In GET_I method read your newly created dropdown field value
3. Based on dropdown field value set the parameter RV_ENABLED(I don remember whether its RV_ENABLED OR RV_DISABLED) of GET_I method of address field as true(X) or false. If its enabled then the field will be in editable mode, if its not then it will be in display mode
Let know if you have any questions
Thanks & Regards
Gokul Ragunathan