It depends.
If you use AltaUserPoints, it must have a plugin or some rule to do that. So you have to configure that in AltaUserPoints.
If you use a custom user field of HikaShop for the points (so without another point extension), you can create a mass action with a trigger "after a user is created" and an action "update the values" on the column of your custom user field where the points are saved with the value 50. You can do that in the menu System>Mass actions:
www.hikashop.com/support/documentation/167-massaction-form.html
If you use EasySocial points, then I don't know. You should check with them what they propose.
