I know that there are bunch of parameters we can define for gazebo in ros launch file

For example:

<launch>
  <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="worlds/mud.world"/> <!-- Note: the world_name is with respect to GAZEBO_RESOURCE_PATH environmental variable -->
    <arg name="paused" value="false"/>
    <arg name="use_sim_time" value="true"/>
    <arg name="gui" value="true"/>
    <arg name="headless" value="false"/>
    <arg name="debug" value="false"/>
  </include>
</launch>

On a similar line, is there anyway to define GAZEBOMASTERURI in launch file?

Please not that setting GAZEBOMASTERURI in shell using export command is not starting gzserver in specified URI.