You may want to change the invite URL away from the one randomly generated by mattermost. To do this:

1. select the drop down next to your username in the top right corner of the blue navigation side-bar (three vertical dots). Select "Team Settings". 

2. Scroll down and select "edit" on the "Invite Code" section. Then change the invite code to whatever you want it to be. (this can also be a good way to cycle invite codes after you've initially on-boarded your team.) Save and finish!