Is it possible to pass parameters to Airflow's jobs through UI?
AFAIK, 'params' argument in DAG is defined in python code, therefore it can't be changed at runtime.
Depending on what you're trying to do, you might be able to leverage Airflow Variables. These can be defined or edited in the UI under the Admin tab. Then your DAG code can read the value of the variable and pass the value to the DAG(s) it creates.
Note, however, that although Variables let you decouple values from code, all runs of a DAG will read the same value for the variable. If you want runs to be passed different values, your best bet is probably to use airflow templating macros and differentiate macros with the run_id macro or similar